I did AFT on the Gnat despite being in excess on 6ft 2in, can't recall being measured for cockpit fit. Years later, when H&S reared it's ugly head, I was told by AMTC that my measurements were such that I couldn't bang out of the aircraft safely.
Ref the double ejection in post 27, I saw it happen. I was walking in with my QFI and we watched the whole episode; we were lucky, the aircraft involved had been the next one allocted by the line after ours so we missed it by one.
If my memory serves me correctly, the tale was as follows. The front seater got out OK, the rear seat pulled his legs back (the story was he was worried about losing his kneecaps on the instrument panel) which inevitably broke his thighs. On landing, helpful holiday makers grabbed him by the ankles to stop him being dragged by the chute, this released bone marrow which had some sort of nasty effect on his nervous system. Happily, he recovered.
As for formation in the Gnat, I thought it was just me!