Rear-view mirror location on a 69 K20 Custom Camper

[CustomCamper69]

I have a 69 K20 Custom Camper and the rear-view mirror has decided it doesn't want to stay on the windshield any longer...bought too many of the adhesive kits from Napa to count. I also have a 69 K20 Suburban, but the rear-view mirror for it is mounted above the windshield. Can anyone explain the 2 mounting locations and any tricks to get the mirror to actually stay on the windshield? Any pics would be helpful as well, as I beginning to wonder if the mirror is supposed to be on the windshield.

Thanks!
Josh