@Ayugene
Differing compression used by the mapmakers could explain it. Even if it slows the unit down a bit and/or resolution is lower, it's a good move to create ~158Mib more free space on units which are now very tight for space because of such a large EU detail map which will become even larger as time goes on.

There are different sized DEM maps for NA too. The original larger one is well over 1GiB and the new smaller one's only 594MiB.