Your submod looks really cool! I was wondering if you have considered looking into how geography and infrastructure could be tied into logistics:
, I was thinking that geography should also be tied to the logistic system. After all, geography is the very reason why we need logistics in the first place. Having ancient armies clashing in the middle of a desert should not be as doable as having armies clashing in lush farmland.
Logistics should be expanded beyond the urban/rural system and also take account of geography by food yields.
1-2 Food yields: Provide no bonus
3-4 Food yields: Expands logistics by 1
5-6 Food yields: Expands logistics by 2. And so on for higher food yields.
0 Food yields: Decreases logistics by 5
These numbers can always be changed for balancing, but the main point is that tundra and deserts should not be able to support the same size armies as lush farm land.
Logistics can also be improved by a few ways: coast/river, great generals, and buildings (in addition to aforementioned technology being an influencing factor)
Traveling by coast/river will improve logistics by 1 or two, regardless of the terrain, as the army is being supplied by “merchant ships”.
Great generals will negate the 0 food yield penalty on logistics completely. This simulates for example the brilliance of Alexander the Great navigating through the deserts of the Persian Empire. Or a great general can have a special promotion line that affects logistics. First level improves army logistics by one, level 2 improves it by 2, and level 4 negates the 0 food yield penalty on logistics completely.
I was also thinking that path improvements (cart path, road, paved road, etc) would also improve logistics and each better path improvement would provide a better bonus for the tile, but that may be too many variables for logistics already. Movement bonus may be good enough reason to use it already. Perhaps a slight terrain defense aid? Soldiers are better supplied by road, so they are better fed and able to fight better:
Cart path-no bonus,+1 to logistics?
Road-1 % defense bonus. +2 to logistics?
Paved Road-2 or 3 percent defense bonus, +3 to logistics?
Etc
Buildings, such as ammo depots and barracks would increase urban logistics.
TLDR: Basic idea is to adapt the logistics system in regards to geography, great generals, path improvements, and buildings as influencing variables to rural/urban logistics.