Could be that there is too much sealant between gasket and body. The glass is suppossed to be a little samller than the body opening. The gasket has approx' 1/8 inch center web that is supposed to be squarly between the body ( edge of pinch weld ) and the glass.
If the glass doesn't seat low enough the gasket has to roll outward at the top.
If you used a sealnt that will soften with heat you might heat it up and shift the glass downward and inward.
By shifting the glass, even climbing up there and sitting on it imediately at install I got all of the top of my notchback rear glass and gasket to seat right except for one place about 6 inches long at the right upper corner. Yes a good bit of my sealnt oozed out.
Weeks later and sitting in the hot sun it has settled more and looks almost perfect today.
Pics show the glass needs to move to the right as well as down