The pop-up I had installed was inalfa model # F700. The glass measures 14.25"x30.5" - and 31.75"x15.75" for the outer measurements of the rubber seal on top around the glass.

I believe the larger one 34"x20" was ruled out because it may have required moving and re-wiring the overhead light. I think the smaller one looked better with the roofline and ridges. Not to say the larger one may work out OK as well.

Hope this helps