It could have also been to improve headroom, and possibly 'dropped' due to production requirements/restrictions for the 'blown' or moulded section.
The basic shape, as a completely 'blown', one piece canopy, without the horizontal frames, would have been a vast improvement, and, I would think, this was realised. However, the capability to do this, with the technology of the time, particularly given the demands and problems facing German industry at this stage of the war,was not as easy or straightforward as it seems today.