Unit size mod doesn't work for the second player

Hello everyone,
I installed the mod where the units have a realistic size, looks great! If I now play against a friend who also has the mod, his troops are still the same size as before, i.e. twice as big as mine. Are we doing something wrong? It would be great if someone could help, because it’s no fun that way…

And is there perhaps a mod for AI opponents so that they can also build walls?