AI not defending its planets?

[Barbagli]

Hello gentlemen,
I just came back to the mod after many years. I go straight to my question:
Playing as the PA, Steam version of the game, Captain level just to retake confidence with the mod. All great. However, is it normal that the AI is barely recruiting any garrison even on its frontier planets?
I agree that we're all here for the super epic space battles, but I actually enjoined a lot my ground invasions and defences back in FoC. This way, planetary battles are quite less epic. Moreover, this means that planets controlled by the AI change hands with terrific frequency, and every time the AI has to spend money to build something on that planet just to have it fell in enemy's hands in one or two weeks.
Is it a known issue? Maybe it's different on Admiral? Might be some issue with the galactic population cap, since I can barely manage to defend my frontiers decently and maintain two big fleets (and leave all the other planets practically undefenfed) before reaching the maximum?

Sorry for the perhaps silly question and many thanks for your work.