Series front door top windows

[RoverKid_1972]

I’ve just installed the sliding windows using our host’s door top kit ( Window Fixing Kit Series Door Top Model #: RNA0349). Once installed, however, the glass alignment seems off. The rear pane slides far back enough that the vertical rubber seal slides past the end of the front pane (see photos). I believe I did the install correctly and followed along a YT tutorial by steamwally. My only thought is that more aluminum shims behind the vertical felt track would fix the issue but look pretty bad. Any ideas to fix or identify improper install would be greatly appreciated.

Thanks, all.