[Crakkerjakk]

Yeah, if someone is totally behind cover, I think it's probably best mechanically modeled as "shooting at the bit of cover you think they're behind."

Then maybe a 9 or less roll (kind of like shooting through someone's hex) plus a random hit location roll, if you're using them?

If the rules say you can't get an aiming bonus because someone's behind the corner of the wall a hundred yards away, and thus can't even hit the wall, that's obviously dumb. So choose a different way to look at it, IMO.