When the target is 22 degrees, in plan that's 44 degrees --close enough to 45.
In my experiment with Zeppelin-izing a Beetle I established a 45 degree bulkhead and found where the gentlest curve to reach it was.
The solid bulkhead is where a boat tail without the reflex curve would terminate. The open bulkhead is at the original bumper location. I think terminating in a vertical line instead of a low point would impart directional stability.
I guess I've never posted the picture, but I established that a Studebaker Starlight-style V-shaped window would not impair rear vision. Cooling would be through the front of the rear fenders. Oversize like Tatra to allow either side to work in a crosswind.