Thanks, I asked for those to rule out a modern reproduction or manufacture at a later (but still vintage) date by a costume shoemarker (either of which can be very convincing). The construction looks period to me. The arch is thickest there because it has to take the bulk of the straps sandwiched inbetween all the other layers, as well as a little reinforcing along the length.
I wonder if the heel just seems bigger than it should be because they are a really tiny size? It's also worth mentioning that modern methods of replacing heel tips actually reduce the height of the heel everytime it is done, because a sanding machine is used to shave the old one off, rather than doing it by hand. Over several repairs you no longer have the original shape of the heel anymore.