combat modifiers: stealth armor + ECM?

[jc173]

Once again a question for those with more experience modding. Is only one component for combat to hit defense plus effective per ship or is only one component per family effective? I guess what I'm trying to ask is does stealth armor stack with ECM? I've done a little testing, and it seems that at least at fairly close range for the same distance for one target with ECM and stealth armor and another target with ECM only I got the same to-hit percentages. So would I be correct in assuming that the game engine just grabs the highest bonus for that ability and ignores all others unless that component is destroyed?

My other question is would a component with the combat modifier - system with a penalty affect my own ships? (Trying to model a larget scale barrage jammer)

Last question: Do Combat Movement components of different types stack up?

Any help/suggestions would be appreciated.