Just curious:

If at the end of a combat turn I leave enough TU's for, say, a snap-shot from all my soldiers, then the chance of them firing is (presumably) based soley on the individual soldiers 'reactions' stat. More often than not a spotted alien (during the alien turn) will usually get a chance to mooch about a bit, perhaps fire a shot or two, before coming under a hail of weapon fire- unless facing my 'crack' experienced troops. Fair enough.

However, I noticed that if I 'camp' outside a UFO door for a couple of turns, without expending any TU's during my turns, as soon as an alien pops his head out, all my troops- regardless of reaction rating (i.e. even rookies)- will all open fire straight away. I mean the alien doesn't even get to drop his note to the milkman or even scream before a dozen or so rounds perform their own brand of acupuncture. Seriously, the enemy just opens the door and WHAM!- doesn't even move or fire.

Is this an in-game mechanic at work, taking into the consideration the staking out of the entrance or merely my imagination?

Edited for guff and misspellings

I'm no expert on opportunity fire mechanics, but I've a feeling there are other factors involved rather than a direct comparison between unit reactions. Time units might be one of them.

It seems that if a unit has more time units, it has a higher chance of getting off a first shot even though it has the inferior reaction skill level of the two parties in question. I've often had a soldier with good reactions superseded by an alien with lesser reactions because it had a fuller TU bar. Of course, this isn't always true.

This is a wild guess, mind, but I'm thinking the rookies, even though they have poor reactions, are performing their opportunity shots because their TUs aren't as exhausted as the alien's is. Sometimes after a volley of shots, the alien will get off a shot or two of its own before everyone resumes firing merrily away at it. I suppose it's because the alien's TUs is now lower than your soldiers.

This is partly why I like to use the laser pistols for reaction fire, as they're quite low on TU consumption, and with 6 - 8 rookies waiting in a generously scattered formation outside a door, you get a fantastic light-show every time the door opens.

Again, that's just a guess.

Hmm, if only there was a way to test things in order to better understand how reaction fire works...

- NKF

edit: After going through what I wrote, I realised I couldn't make out a word I was saying: Reworded some bits

I'm no genius on the game, but using more logic than anything, I could say it like this.

If you are camping out in front of something, simply WAITING for it to come out, even kids with a reaction of like 30 will fire. They have the TUs, and realistically speaking, they're "Tense and ready for the moment"

Now, I have no idea if this was intentional or not, but it just seems to work that way.

A question of my own would be:
Let's say that you stop and kneel with like 25 TUs left with the purpose to save for a snapshot, and stuff, and then here comes an alien :alien2: so your soldier sits thre with his gun and gets his reaction fire :devil:, now my question: if you have enough TUs for an Auto shot, will it use that or just a snap shot? Does it take the one with the higher accuracy or higher TUs?

Good point- that was going to be my next question.

It's quite hard to tell during the alien's go. If a trooper fires three times on reactions, is it three seperate snapshots or one blast of autofire?

I'm fairly sure (that is so far to say that I am not really sure at all) that in XCOMAPOC it was based on what 'reserve TU's' settings you chose for each soldier. The game would remember your preferred settings (e.g. Agressive, reserve snapshot, etc) for each individual soldier and seemed to apply them in reaction fire scenarios. UFO doesn't give the impression of following a similar game mechanic (not suprising as the older original XCOM incarnation)- the 'reserve' buttons always default to none selected at the beginning of a turn and apply your selection to the next selected soldier and so on. With that in mind I suppose that the computer makes a decision based on soley the number of TU's available.

I'm sure that sensei NKF will be able to clear this up for us.

Time units have a definate effect, no doubt about it. I observed this on many occasions camping outside doors. My officers with high reaction shots would fire first, but the rookies would still fire.

I estimate that it counts about 70% TUs and only 30% reactions as a basic rookie, but that changes the higher their reactions are.

The reserve time unit buttons aren't just for reaction fire. They're for reserving time units so that you don't run out of them before you end your turn so you can at least get off a shot (you might have noticed that the reserve buttons won't stop you from shooting).

As for reaction fire in general, I'm not entirely sure how the type of shot is determined. From observation, it's always been snapshots. Even when a unit goes berserk and gets a temporary 255 TUs to spend, it's always been spent as snapshots.

But then again, it's best not to discount the possibility that auto-shots are sometimes used. I've a feeling I've seen a cyberdisc use its burst mode as opportunity fire against one of my soldiers once.

- NKF

Unless there are enough time units for 3 snap shots, which with the heavy plasma, is not possible, then I see many Snakemen firing auto-shot reaction fire at me, which is very annoying.

I think it ought to be possible. Heavy plasma snapshots only use 30% of a unit's total TUs to fire. Should be enough for any unit to get off three shots and still move a step or two.

- NKF

On a few less related notes:

It's funny, but all the plasma weapons need the same TU percentages for snap and aimed fire -- 30% and 60% respectively. It's only the autoshots that differ. With rifles being the slowest, to heavy plasma being in the middle, and the fastest being the pistol. On the other hand, the rifle is also the most accurate auto-fire weapon in the game, so it's no wonder it's more expensive.

Also, despite its name, the auto-cannon is the slowest auto-fire weapon in the whole game. Funny that.

Another determinant could be skill setting of the game, initially wen i played the game on verteran i would be able to pull of reaction shots before aliens got outside of the door, however, wen i play on superhuman (cauz its harder ) i find that the aliens will usually get out kill a man and then my troops will reaction fire...

Once i had an alien who kept shooting the door of their UFO, duh! the door needs to be open first... It was the last one and it ran out of ammo and it started to panik and threw a grenade inside the UFO... Poor fella

I'd say the equations look something like this:

if (movement TU by alien + shot TU of alien) < ("reaction" TU of soldier + shot TU of soldier) : alien fires first

But I think the time spent opening the UFO door is added to the movement time. Same for your own soldiers going through UFO doors. So this is very slow, and the following equation generally comes up True:

if (time to open door and step outside) > (reaction time + shot time of rookie x camped outside) : rookie x gets to fire before alien takes next action.

Alien reactions either a) might only apply during XCOM's turn, or B) are compared with XCOM reactions. No idea what governs auto-fire reaction shots.

TUs are also a part of the equation. I've just fought a base defence mission where i had the corridor leading into the airlock filled with soldiers on the sides, both rookies and veterans. Everytime a rookie with low TUs would step into the corridor and into a Sectoid's view the alien would immediately fire. If it was a veteran with high TUs he would be able to fire before the alien responded.

And i think alien TUs are definitely a part of the equation also. The skill setting of the game increases the alien's stats.