So, managed to fix the seating position...
As I previously said, the Recaro Pole Position seats are, on their lowest setting, significantly higher than the stock seats. I kind-of got used to them like this, but since I fixed the steering wheel I said I could fix this as well.
So, I manufactured some side mounts, about 3cm shorter thinking it would solve the problem. But I didn't. The seat base would come in contact with the horizontal part (base) of the side mounts. In fact, by making the base thinner (as the original base was, in parts, wider), I could lower the seats by about 1.5 cm. This was clearly wasn't gonna cut it. But there was also a seat belt mount (for the OE seat belt buckle) what increased the seat height by 2cm.
I decided to cut a whole in the side mounts and fix the seat belt buckle to one of the side mounts to seat rail, bolts. So, I basically removed the need for the extra 2 cm seat belt adapter.


I also changed all the nuts and bolts (with 12.9 grade bolts), powder coated the side mounts and bought RECARO stickers.

As such, here is the before and after.


The wider washers are more visible in the second image but, except for that, the mod is, visually, indistinguishable. Which is exactly what I was looking for.
Overall the final decrease in height is
3.3 cm which clearly makes a huge difference - "that's what she said, right!?"
I quite like the new seating position but I have to wait for Spring to truly test the car.