Need some help on rear window weatherstripping and install

We've seen this before. The factory service manuals state that the top of the window goes in first. Soooo, how we install could be a factor. Me... I wouldn't want the gasket lifted away from the package shelf either.
I know the center web of a aftermarket gasket could be a tad too thick and just maybe the replacement glass is a tad too large. The simplest and really the only thing we can adjust is the fence that the gasket sits on. Using a grinder to trim that fence ( a sixteenth or so all the way around ) kinda equals rough framing a window opening in a wall. Must be the carpenter in me. LOL