Well, just looks like ol' Battle Isle on the Amiga; except that in Battle Isle units moved 5-8 hexes per turn (depending on unit type)...
So I'm going to change Units movement points (like I did once while playing Civ 3 a long time ago);
Perhaps they could prepare Civ VI with cities of 5 hexes length, and you could enter a city with troops while it is still defended on its central hex...
I still regret that Sid Meyer's team did not purchase "Conquest of the New World"'s battle system, with armies consisting of three types of units (soldiers, cavaliers and cannons), soldiers moving 1 square per turn and cavaliers 2 squares, cannons left beneath but hitting at range, and there's a 25-squares grid where units battle each other, with a central square on each side reachable to gain victory on the opponent. :( (still I just *loved* Battle Isle :) )