Actually, they don't as Gillette held good specs for a non-CNC World. I have measured the blade gap on pre-war, post-war, ball end & English (flat bottom & ball end) and they all were within approx. + or - 0.002". That's damn good for today, let alone mid 20th century.
Personally, I don't think there is any difference in how they shave except that the post-war has better blade rigidity and shaves ever so slightly smoother. Blade gap/exposure is the same on all aforementioned.
Then it must be about the angle.
The Fat Handled Tech I have has a wider bottomplate than my Ball End, 25,5 mm for the Fat Handle and 25 mm for the Ball End.
The difference between the topcaps are 0,1 millimeter.
The difference in their handles can play a part as well.