One of the things that bothers me about this game is the inexplicable advantage Attackers get when invading a planet. I haven't bothered with any hard statistics, but it is extremely obvious to me that attackers get some huge inherent advantage when attacking. For instance, as a rule I tend to make sure I develop all the invasion techs (with soldering bonuses) and the Tri Quan training facility. I have no problems taking out planets with 10-15 billion with an invasion force of 2-4 billion under most circumstances. Now, in the same game, if I happen to let an enemy transport slip through, they might have 1-2 billion on the transport, and yet they manage to inflict at the very minimum, casualties on a 1:1 ratio, but often closer to 1:2 or even 1:3 (in their advantage). So how is it that I can invade a planet with 4 times the population of my invading force, and wipe them all out, while that same AI can invade one of my planets, being outnumbered 10 or 15 to 1, and inflict such lopsided damage?
One of the most well known rules in war about attacking is that you should at least outnumber your opponent by at least 2:1 before you consider attacking a hardened defender, but this game does not seem to follow any logic in this regard.