My Thanks to Augusto and Pete W. for your suggestions. Renaming worked like a charm.
Broadsword, there is one problem, which you already probably thought about. Because the battle map "lies" on top of the "distant ground" tile, whatever one of those you use will extend out to the horizon. This means that a ground tile will just show, well....ground, all the way to the horizon. If you use a modded one to represent water, then when you zoom up from the map, it's surrounded by the water tile up to the horizon, which is fine looking north, but pretty funky looking in any other direction.