[Q]

Another IMO odd feature of nebula systems (or any cloaked sector/system): If you can see the enemy because you have sensors that are potent enough but the enemy can't see you, your fleet will cowardly not engage the enemy if he enters the sector your ships are in. Therefore it is pretty useless to put any defences on warp points in such systems with cloaking abilities (with the exception of mines). You can only engage in combat if your ships are entering the sector where the enemy is, but then of course you loose the advantage of the defenders first move/shot and you can't do that with satellites or bases alone.