Tim, I think the flattened rear canopy was "known" as the Grace Hood after the late Nick Grace who designed and incorporated it into the rebuild of ML407 for exactly the reasons you describe.
But if memory serves it was cited as possibly a contributing factor to the sad accident which beset PV202 and her crew at Goodwood a few years ago because the vis is much poorer for the rear occupant - who was instructing at the time - compared with the Vickers style canopy with which 202 has recently re-emerged.