To attach any piece of pyro-glass, you need a hard shelf at the bottom as a mechanical form of security. That way, if the chemical (epoxy) bond is compromised, it stays put.
I held my glass to the platen where I wanted it, and marked two spots to drill and tap for two socket screws like these:
Size is unimportant. Just make sure that the glass is thicker than the heads so the heads don't impact the belt, and be sure they are level across so the glass edge sits against them and is still aligned with the platen.
I then cleaned all my bonding surfaces and used my normal epoxy for the job. Use plenty so it self-levels and be sure to get some on the screw heads and bottom edge of the glass to secure than connection.
I've been running like this for about a decade (give or take a year or two) with zero issues.