XK120 boot/trunk lid trim

I would like to know why the trim doesn’t cover the entire underside of the boot lid. Why is the lower 6 inches left open?
I’m thinking of using my old skin rather than mdf or millboard as I hate throwing things out, much rather repurpose it.
Any ideas much appreciated.

I believe that, in part, it was to accommodate the spare tire position differences that arose because of minor variances in the gas tank mounting, padding, etc.

Simplicity cheap part of tire poles into the area and the boot lock bars are lower so it would have need to humps.
I did retrim my first car back in 1977 and did run the board down either side but not centre and have seen cars like this with no panel behind but just vinyl spread over area so tire can clear