Qingqi QM200GY-BA (Qlink XF200) alternative rear shock

[forchetto]

The only thing standing in the way of total happiness with this bike is the seat height. I'm running with the rear shock on its lowest setting, have sliced 2 inches off the seat foam, and can now just touch the ground with both my toes. As the bike is very light, it's easy enough to handle like that, except when manouvering backwards to get out of a parking slot or similar, or when I have to stop at the side of the road and the camber or edge of the roadway isn't very level . I could do with 20-30 mm less ride height.

The only alternative I can see is replacing the rear monoshock with a shorter one, at the moment it's 335 mm long from eye to eye.

Buying a shorter one is not as easy as I thought. You can't just replace it with a 20-30 mm shorter one just like that as the bottom part of the shock is attached to a linkage that means that up and down shock movement is not proportionally the same as the resulting wheel movement.

How could I determine the total new length of the shock to give me those 20-30 mm on the ride height that I'm seeking?. I know it's bound to involve maths and geometry and I'm a bit dumb with that.

This is what the shock and bottom link look like: