Thanks for the photos. I was wondering about the first photo of ebay and here it is, from a first generation car. Also, the photos you have from the tray, I have seen them on ebay and I was also wondering from what car they come from.
Your car has a subwoofer. This means it has a different tray than my car that has no subwoofer. The tray in my car is full of deep spaces like yours have on the side only.
What I meant before is that for the a moment, just put aside the thought of the tray and just remove the subwoofer and fit the spare wheel. If the first and the second generation cars share the same spare wheel, then the subwoofer should fit in the spare wheel.
That is how it is described in the older posts. So once you have done this setup, subwoofer inside the spare wheel, you will be left with a few centimeters of space. This space is the height of the foam tray on its thinnest points.
So my understanding is that you need to cut all the long pieces of the foam and leave the thinner parts of it to sit on top of the combination of spare wheel and subwoofer.
Even then, the thinnest part of the foam may need trimming. So to avoid all this, in most old posts, they bought a wooden flat surface to fit on top of the spare wheel and add the carpet on top of it.
The problem is that if you fit the spare wheel, there will be a hole inside it. So the carpet will drop in. As a result, you need something to support the carpet.
If you have a subwoofer, you need something to act as a barrier between it and the carpet as you can damage it when you load the cargo space with weight.