It's less clever, but you could remove the "same terrain" concept and just make the border growth trigger 3 free tiles too.
vs.Cities gain 3 additional Tiles upon Founding or Conquest, and claim adjacent unowned Land Tiles after borders expand to a Tile with the same Terrain.
Cities gain 3 additional Tiles upon Founding, Conquest, or expanding borders naturally.
Combat Strength in friendly territory.
1
for each Encampment if it has a Smokehouse, +1
if it has an Interpretive Center.
at rifling
Population, Cities give birth to Taikwahni instead of new 