Another day spent trying to improve the door gap situation :)
First of all, I decided to solve the root cause of a lot of the problems I am having by slotting the hinge panel. Then the A panel could flex outwards in the middle and match the profile of the door skin. The door was now free to open with a bit more room to manoeuvre without the door skin catching the A panel, and I was then able to work on closing the gap a bit more. Joys!
Then I ran a filler rod down the front door edge.
The top bit needed a double thickness to close the gap.
Much faffing around later, I am getting a much nicer gap. Still some tidy up to do but I'm pleased with the improvement so far.
The big turning point was realising I could adjust the gap in-situ. I added more than enough filler rod to the door, then with the door mounted in position, cut the gap I wanted by carefully running a 1mm cutting disc between the panels. Felt dangerous, but gave me quite an even result.