The early 'blown' canopy of the Mk I is not to be mixed up with the later Malcolm canopy. Effectively, the early canopy gave very little headroom and later a very small curve (about and inch or so) was added to the top. The canopy was still very narrow, so the later Malcolm canopy, introduced in 1941 or 42 IIRC, modified this early canopy with a wider, sphere-like section in the middle section. Otherwise it was similiar.