How do the mine placement work? Just random?
Possibly. It's not in the maps.
So I have images of all of them. There are 13 locations of maps in memory, but there are only 6 unique ones and one of which is completely unused. If I'm not mistaken, that means that the ones that are copies can be replaced and that frees up literally 4K per map for additional data for use for modding.
So according to my viewer:
0x981000 = 0x982004 = 0x994708 = 0x996F10 (yep, four identical maps)
0x983008 = 0x991F00
0x98400C = 0x98F6F8
0x985010 = 0x98CEF0
0x986014 = 0x98A6E8
0x9874F0 is unused
Removing those dups (as well as pointing their current pointers to a common map) and the unused one will free up 32K worth of space. It's not contiguous.
Best you could get is removing 0x981000 - 0x987017 and getting 24K of contiguous space out of it.