@HungryForFood has intimated that he might start work on a major alteration of the Steam Mill for his
Victoria for CBP mod.
If he completes work on that bonus, whatever it may be, I would be inclined towards just matching it in 4UC. Until he has a more firm idea for the new bonuses I will sit tight, but he suggested he might try to make a new DLL table which gives constant yields in the city for every

TR in/out of the city.
More specifically, he was contemplating +2

for every TR in/out of the city