Ah, so reinforcements don't just magically appear at Guard Posts? A reinforcement warp gate must be there to allow that to happen?
So if you go in, take out all the reinforcement warp gates (including the command station, rendering the planet neutral) but leave all the guard posts, the AI will no longer reinforce the planet?
If true that would make an early-game raid starship blitz on many alerted nearby systems very appealing.
So reinforcement warp gates determine whether the AI can reinforce a planet, and guard posts determine how many forces the AI is allowed to station there?