Alright back to topic, the dilemma is the speakers are placed on a shallow (and high-ish) mantel (~60" off the floor). The mantel measures 10.5" deep, but there is some trim column work that interferes with part of the depth where the L/R are situated. With the column interference, the Sierra's would be spaced 2.5" from the back wall. This would then result in them overhanging the mantel in the from 2.5". It would be possible to use the mounting screw to fasten them to the mantel to avoid a potential gravity mishap. Not much appetite for now in moving to a floor standing configuration.
Overall this poses an ominous situation and a need to consider room aesthetics.
Certainly welcome other's thoughts and experiences as well. Thanks for any ideas.