Its the mounting point that is problematic because it is so high up on the side, makes the start point high for aftermarket rails as you'd want to drop the seat down inside the pillars, I have similar issues with seat height in the MX5 which I solved with a seat and rail mod but I don't see easy options here beside cutting the mounts down, perhaps a Tillet with the saggy arse base I forget its name B5 maybe,will work but would not want to daily drive on that)
Someone's height is not the issue so much as how they sit and the body composition, I am only 5 11 but sit like Robert in that vid, upright, plus being a long torso, short legged wierdo, I have less head space than him, so I am really interested in what comes out.
On one of the sites I found some one who had stripped and weighed a lot of parts and also fitted some normal looking seats lowering by 6cm, that would pretty much solve it but can I find that link again.....grrrr.