An elegant way to make the Goth Imperial Age pop cap bonus respond to map size

Currently the Goths have

• +10 population cap in Imperial Age

this is balanced around (I presume) a 200 pop map, so it's effectively +5% population. This same effect could be achieved by changing the amount of population each unit takes from 1 to 0.95238 (in imperial age). This would make it responsive to map size (e.g. in a 500 pop game Goths would be able to produce floor(500/0.95238) = 524 units).

The main problem with this would be that it would be slightly confusing for some people. The "elegant" in the title refers to the mathematical/technical perspective of this solution (rather than the user/player perspective of the solution)