Hi @Obioban
There isn’t a specific distance mentioned in the product guide, so I can’t give you a range, but I think common sense will serve you well - you obviously don’t want them to be 20 feet behind you, but you do want them to be behind you rather than directly above you. If your couch is up against a wall, it may be “best” to pull it out from the wall a foot or two so there is space to get the speakers behind you.
Please note that we do recommend normal mounting over inverted mounting - it will be a better experience - so if you do end up pulling the couch out, you may want to just mount the speakers at (sitting on a couch) head height instead of inverting them near the ceiling.
I hope this helps.