The seats from 2003 - 2007 with the shallow dashboard had tapered spacers which were at chassis rail height at the front - so 2.5cm, and half that at the rear. Obviously over time, owners may have removed or changed them, but removal gains that much space.
From 2007 and the deeper dash there were no spacers, but a protruding nut under the runners means that there is some distortion which stiffens the adjustment. On my 2017, I've added some shallow spacers (around 1cm) to level the runners, because I'm short so I don't need space between the seats and steering wheel.
Heated seats can be retro fitted.
