I've noticed quite a few people mounting them backwards on this forum, (I believe I saw a PRI front BUIS mounted backwards recently) and some people do it for preference. (Easier to get to?)
I personally prefer to run them the way they're meant to, but to each his own.
Nothing wrong with mounting your BUIS backwards. They zero just the same.
"Amateurs talk about tactics, but professionals study logistics." - Gen. Robert Barrow, USMC (1980)
I do it with my eotech all the time...
Riding, Shooting, or Golfing...you pick and I will be there.