Stack of Coins and Income Level

[tinkthank]

I'm sort of confused as to the height of the stack of coins shown on the map and the corresponding level of income.

In one MP game I am playing, my dominion reaches to some areas still owned by Indies, and I can clearly see the stacks of coins and also get a reading for resources and for income. Lots of coins, lots of income, fewer coins, less income, everything fine.

In one province, however, with the least amount of coins possible (two) I get an income reading of 17 (which seems quite a lot), while another province nearby has more coins (about 7, the next step up I think) but has an income reading of 4.

I thought that more coins means more income? Is there something odd going on here?

thanks in advance