A ROM extension must be 2 KB-aligned, have a zero checksum and must not overlap with another ROM (I leave aside builtin modules).
In principle, BIOS might violate some rules, for example, refusing to scan a desired memory address at all. Try a different one, let's say, 0x8000, it is 32 KB-aligned.
If there is still no effect, dump the 64 KB memory block starting at 0xe000:0x0000 in the running system, I'd like to see whether XT-IDE is really there.
As for another machines, I don't know how exactly do you embed XT-IDE in every particular case, it is hard to comment what could be wrong.