best not to get too obsessed over it like I did...! But worth re-reading this https://aus7in.wordpress.com/2018/11/17/...n-and-fit/ if you ever have to sort one out that plainly needs repair.
Assuming Austin wanted rear wings central to axle because thats what the 1933 plan suggests (but didnt actually properly achieve it until the later Nippies, when the wings changed subtly) the only other option after "that" panel being smaller is the body moving forward.. so you can assess that in relation to the starting handle nose piece, steering wheel gap and so on.
You can see here the 1933 test car image, admittedly from a poor angle. That panel is narrow, but even then, the finished wings weren't of a radius to allow the 65 to be visually as per drawn plan.
By 1936, they were!
Assuming Austin wanted rear wings central to axle because thats what the 1933 plan suggests (but didnt actually properly achieve it until the later Nippies, when the wings changed subtly) the only other option after "that" panel being smaller is the body moving forward.. so you can assess that in relation to the starting handle nose piece, steering wheel gap and so on.