Are you replacing the top?
When I replaced my top, I lined the rear bow up to the seam and stretched it from there. First I loosely attached the front and then I stretched and got the rear area smooth and then readjusted the front edge. For that I kept loosening and tightening the front edge until the top closed as it should.
I would measure it for you but currently my convertible is a very large storage table.
If you would like me to measure something I will be glad to but there is a lot of stuff on top of the car so the measurements may be off.