Ok, I am looking at supply and want to make sure I have got it right. It appears that towns are producing supply units at a rate of 8 per city level, 4 per depot or harbor and 2 per fortification. However unlike most Ageod games, a supply unit appears to only produce 1 supply point instead of 5 supply points.
So it seems most cities don't produce enough supply to maintain larger armies. By themselves, most cities/towns can only supply smaller forces. However, there appears to be a strong push of supply into cities/towns which have more troops than can be supplied by the city itself. To get a push of supply into a city/town, the player must maintain at least one supply line with at least 51% military control to the greater world. The more supply lines the better. It also seems the supply push only goes three or four regions and bad weather/road/terrain types have a significant impact. Basically we need some type of supply structure or wagon every 2, 3 or 4 regions plus the 51% military control to ensure a push of supply to a larger army. And if we stop getting supply, something is effecting the supply chain.
So have I got the gist of the ROP supply system? If correct, I really like the importance and vulnerability of maintaining a supply line. I could see how it would make for some interesting operational maneuvering to cut or protect supply lines. Since by themselves most cities don't produce enough supply, armies are heavily dependent on that supply line chain to outside sources of supply. Definitely a major factor in the 2nd Silesian war with Saxony neutral.