Do you need to rescale models for landscape Z Scale Change?

I’m reading a lot about issues regarding changing the z scale on the landscape, stuff like decreased precision, collisions… since the max height is 512 on z scale of 100, I’d like to understand the issues i’m facing by getting my map to about 2km max altitude…

So what exactly does that mean?
engine can’t detect collisions at high altitude? Does this happen only in the air or relevant to land too…?
more chance of falling under the map?
And most importantly, if I have two different maps with different z scale (100 and 400 lets say) do I have to rescale all my models in one of the maps?