How about -just- reducing the ripple effect? Rather than the absolute
Civ - 1 boundaries (i.e. if main province is civ 5, adjacent is civ 4,
adjacent to that is civ 3, etc.) you could use Civ/2, rounding down.
The heavily civilized areas still get a bonus which distributes, but
the curve is steeper, and the effects stop sooner.
A linear example:
0 0 0 0 0 0 1 2 5 10 5 2 1 0 0 0 0 0 0 rather than
1 2 3 4 5 6 7 8 9 10 9 8 7 6 5 4 3 2 1
--kdc