108 inches on the forward leg of the rear railing (orange arrow on the photo), 100 inches at the front edge of the stern perch seats.
My boat and several others I've seen have the bimini arch running almost parallel to the push pit forward support. If I were building a new bimini I'd prefer to attach to the top of the railing (yellow arrow) and follow the yellow line. The forward bimini arch could attach (red line) to the existing rail forward support.
Seems to me it would be less cluttered and stronger.