While going through DarthMod (nice work) I ran across these entries..

default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_AUXILIARY 0.1
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_FRIGATE 0.3
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_GALLEY 0
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_INVASION_FLEET 0
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_LINE_OF_BATTLE 0.5
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_MERCHANT 0
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_SPECIALIST 0.1

It seems to me the AI balances it's type of fleet based on this and they all must add up to 1 (or 100%). I happen to be a programmer and I got into it by modding, so I love hacking for stuff. Unfortunately, the thing I don't have is time as I have two hard deadlines that barely allow me to play, much less test. I put this out there that perhaps, PERHAPS that making the invasion fleet for say .4 or .5 and balance the test, the AI might "get it". Something like this:

default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_AUXILIARY 0.1
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_FRIGATE 0.2
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_GALLEY 0
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_INVASION_FLEET 0.4
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_LINE_OF_BATTLE 0.1
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_MERCHANT 0.1
default RECRUITMENT_NAVY_CATEGORY_BASE_PROPORTIONS_SPECIALIST 0.1

I would boost the merchant because it seems the AI puts only one or two merchant ships and ignores it afterward on trade outposts.

I put this out there as a suggestion and hope someone "runs with it"
Thanks