Hi,
The placing of lr is a personal choice I would go for originality and cave structures but as was mentioned keep it away from the glass so cleaning is easier and more importantly in my opinion ensure water can flow round almost all of it.
Think of the rock security as rock falls are fine in mother natures orbs but potentially a nightmare in the fish tank, when rock falls against glass and scratches it it creates weakness in that area and if it falls hard enough a phone call to the insurance company will soon follow.
Seasons greetings
Ricki