I do find it a bit odd that the allied ships enter the atmosphere and participate in stages 4-6, but the Imperial ships do not.
I also find it odd that the Imperial commander has Int 3, Cunning 3 and Knowledge (Warfare) 4 and uses very dull and predictable tactics. IMO, he should at least throw a few curves at the defenders once he sees he has some opposition rather than just plodding forward in a predictable manner.
The GM could definitely change that if so desired
I think it would be useful if there were suggestions on how to change tactics like rebels do X the imperial commander does Y, so the GM has guidelines on how to adapt to the player's actions.