I'm always extremely wary of post-mortem criticisms of hated figures. Especially when that criticism is about physical characteristics. Just way too many instances in history of people making shit up after the fact like "and he had a small penis too!". Take the supposed autopsy of King Charles II of Spain which includes such gems as his body "did not contain a single drop of blood", that his heart was the "size of a peppercorn", and he had "a single testicle, black as coal".

Not saying the people making these claims on Hitler are wrong, but it sounds very similar to other instances of historians not letting the truth get in the way of a good story.