If I may, admittedly as one with little expertise in WFO design, this seems to be in a very theoretical space.
Pragmatically, having experienced the throat reducer, there is a point where it is simply too much of a pain in the butt to use it if the door height is too low.
It seems to me that you can probably design a throat reducer that will also take on the effectiveness of a draft door. But, it could be so low that I would give my oven away to a neighbor. Maybe not, since I could use little skinny sticks of wood to get in the oven and move them around and since I try to keep the thickness factor low, so I guess it is still possible I could get a pie in and out of the oven.