I think the gag Lucas and the animators had in mind, because Jango hitting his head on the Slave I door was done in post-production by the animators, was that Jango hits his head on the door often. Since Boba is an exact clone of Jango, he has inherited his father's poor depth perception while wearing the helmet.
And they further tie/retcon that into the Stormtrooper in A New Hope that first hits his head on the door on the Death Star, suggesting that this particular Stormtrooper was one of the last remaining clones created from a thinly stretched sample of Jango's DNA.