Oh, interesting, didn't think of that.
But that isn't really significantly different from what you intended, as both are precisely-timed bombers. I should also note that as it is right now, I think things still work if the bomber explodes right after it lands on the lower ledge rather than in mid-air. That too can probably be fixed by extending the upper ledge's right edge more to the right (which I haven't done).
I silently, and without asking, did the change mainly because of the issue of building off the sphere on its left edge, which means you can use the bomber elsewhere, a potentially much more serious issue.
On that note, for backroute checking, I think the key thing to look out for is the use of a skill in an unintended location thereby shifting skill availability in other areas of the level. An example would be to use the blocker on the entrance area instead of building. I believe I've gotten that taken care of (but check for yourself and decide).