i never understood why enemies facing a landing craft is so wrong, i know real life doesn't matter when playing a game but realistically if a troop carrier is landing and you are in the ground the first thing you are going to do is shoot the first idiot that pops his/her head out. Heck even with rules in place for war, enemies will shoot and kill non-combatants. because you know what there are NO RULES in war.
Think about every single war/battle scenario the "home advantage" goes to the one that is there first, Aliens are there and since an approaching craft is coming you would think they will be like "hey lets get ready!!!"