The gap illustrated by your shot including the handle shows that side of the frame is true, as the similar gap above and below the hinge and a clear gap between the light and the frame at the pivot point are the same, yet other photos you've posted show minimal gap between the light and the frame.
To my mind this indicates that likely the light is marginally too small for the frame, a photo of the entire window would help since with those hinges the light presumably can float between the two uprights of the frame.
Agree too that usually the hinges would be inboard for security reasons and that split Aquamac-21 between the leaves would provide a draughtproof wiping seal however retro cutting a suitable groove for it will be challenging unless you can take the frame out and flat-pack it.
FYI I have numerous reels of Aquamac-21 FTAGH if you want some, I have black brown and white
FYI I also have a yet-to-be advertised spindle moulder and Aquamac-21 cutter + other tooling for sale, albeit a significant over-kill for such a small job!
