Middle fastner of the tenax, or middle ie center popper in center of car?
Anyway, mine has 8.25 between the hold downs, 5.5" between the pop fastners.
6 3/4" between the furthest forward tenax and middle, then 4 3/4" between the middle tenax and the rearmost, both sides the same.
I did have a B roadster cover a while back that was slighty larger with a bigger gap between tenax/tenax and popper/popper.
Hope this helps.