How far above or below seated ear height does a reflective surface have to be before it's less of an issue to treat?
The speakers are on 46" Sound Anchor stands,angled down 8 degrees,which puts the speakers tweeters' height at about 59".My seated ear height is 49 1/2" and 6ft. from the LCR's.The glass surface is 29"L x 22"H and is about 3" inches above seated ear height and 4ft. centered, behind the listening position.If the speakers are at ear height, and the glass is located above ear height, specular energy is going to be incident on the glass at an upward incident angle, and the resultant reflection off the surface will be oriented in an upward direction; not downward towards the head.
You can of course dampen any surfaces you want if the goal is to simply deaden the space. Or you can address actual detrimental high gain specular reflections that are actually of issue in the listening location...the choice is of course yours.
But I would suggest that the process and results will benefit from the identification of ACTUAL issues rather than simply potential issues. Not only will the required work and associated cost be less, but as a result of the retained energy in the room, the acoustical results will be improved as well.