maybe it works that way in the original... but I come from Heroes of Might and Magic V, and there are arenas of a larger size (like 14x14)... so, in my opinion, the author should keep the current speed.
Ask the Heroes of Might and Magic V players what the maximum grid size is! Otherwise, everyone will start talking about the terrible imbalance again!

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Неудачное планирование ведёт к неудаче ...
NCF - мод, добавляющий дополнительных существ в HeroesV 3.1