Hmmm just found this in another thread:
http://galciv3.gamepedia.com/Ground_invasions
So, based on how its set up-- the more developed a planet is the less likely it is to defend itself... (because you divide defense by the number of tiles). As development also tend to correlate to population, the argument could also be presented that the more population and factories a planet has the less likely it is to hold out...
Why would the only defenders have to "spread out"-- why wouldn't the attackers have to do likewise? In fact why would anyone spread out? Other than versus tactical nukes (which in this milieu could be an option) standard tactics for any military engagement is to concentrate forces at the points of attack-- both for defense and offense.
I think the game wrestles with a lot of different aspects and i can appreciate how some things might be difficult to design. But... the current method for planetary assault seems a rather half-baked idea. It may not need a major overhaul, but some kind of tweak is definitely in order. Something to change that a very developed planet is less likely to hold out than a less developed one. Plus I would think higher casualties for invaders; right now it seems to me that one transport is all you ever need. What bugged me as a player wasn't that my 2.6 pop defenders lost to his 2.5 pop invaders-- I can imagine enough 'fluff" to allow for planetary insertions behind the enemy or guaranteed resupply, or even orbital bombardment would be a major advantage-- but, what bothered me more than anything was that he took negligible casualties against a larger force fighting on its home turf.
