Thanks! This is very illustrative, just like I wanted. (Was too lazy to search myself, of course.)
As expected, it's pretty tight in there. I know that rural people of old were much more fit than I am, and I would get cramps in several muscles of each leg and in my sides after three minutes in there.
I guess that tall people could build bigger ovens for themselves. Also oven usually has some extra space inside, so it's not as tight as it looks. But yeah, of course it's not something one would do other than of necessity.
