Apparently ECM and stealth/scattering armor do not stack their effects. What we're not clear on is whether they are SUPPOSED to or not.
If MM intends the effects to be cumulative this is a bug. What I'd like to see is a defense benefit for being cloaked. Even if they can see you and attack, surely being cloaked affects your defense abilities???
The system combat modifier only affects YOUR ships. You will only hurt your ships, not change your enemy's combat ability by using a negative value. It would be smarter to use it with a positive value and call it a "System Command Center" or something, a military HQ that coordinates combat and makes it more effective.
No, combat movement does not stack. Only the types of components that are destroyed on use (emergency energy, emergency supply) stack their effects. And standard engines, of course.
[This message has been edited by Baron Munchausen (edited 10 March 2001).]