Jamming effect likely has an influence on missile turning rates. How much, I don't know. But let's say it is percentage based. An evasion matrix would reduce a Janitor Missile's 24 to 19 while a cloaking device would reduce it to 4.8.
Assuming the jamming effect activates within a certain radius of the craft, the effect of a 24 dipping to 19 may not make a great deal of difference at such close range.
I know what the Cloaking Field does. It makes missiles targetting the craft not turn at all while the ship is visibly cloaked. They appear to turn at the normal rate while it's visible (the cloaking drops for a short time after a craft fires weapons).
My own tests (based on telling craft to shoot each other) haven't shown any effect from the Missile Evasion Matrix, but without code access I can't verify whether there's something beyond my sensitivity of measurement.