Bill Tindall, E.Tn.
"Is those arches with a bit of flat in the middle. I would try a really long flat ellipse, then split the arch across the top pair of doors,"

I don't understand. Are you saying to make the sum of the top doors an ellipse, divided left and right half of the ellipse between the door tops? If so, I have struggled with this concept all afternoon with no success. For a reasonable height of the ellipse used to achieve this result this height is spread across too many feet and the curve is so flat it seems straight, except at the ends. The idea sounds worthy of evaluation but I could not make it work. Or I don't understand.