This is only ever seen on indoor maps, which use wall values. It should behave in a similar way on outdoor maps, using the 4 layers instead of 4 walls, but it's hard to be certain without an example. In some single maze maps, the X and/or Y values are incremented by 16 as if they were the second half of a multi maze map. See MAZE0054 for example. This seems superfluous and easily ignorable. Tests which set it back to the expected sub 16 value made no difference in the result.