You don’t increase spring rate just by decreasing length. The rate of the spring is already determined so you can’t change that without swapping springs. Your are linear, some are progressive rate. Pre-compressing your spring increases “effective rate” decreasing travel, and requiring higher damping rates to keep the wheel incontact with the road. The damper you purchased is “matched” to that specific rate and can only be changed if you pull the stack washer valve and build it to different spec using different size apertures to get the fluid flow rate you want.
As for your setup, and unfortunatly most JDM shock manufacturers, you have a certain number of “clicks” on your shock. What I was saying before is most of those click do nothing for your dampening rate…if you have 30 available clicks, maybe the middle 10 or so have meaningful changes for dampening rate. The other problem is they are often not repeatable, meaning if you adjust them, then readjust them you will not end up with identical settings, proven time and time again on a shock dyno.
So for your setup, running the damper on full soft makes the whole thing underdamped for the spring rate. This wears out the internals and doesn’t allow the suspension to follow the roads properly. Setting it to full hard does the opposite, overdamping. This means that when the suspension hits a bump the spring can’t push the wheel back town to contact the road, leaving the tire off the ground (or at least unweighted) for a split second. Again poor handling characteristics. I’d keep them somewhere in the 30-60% stiffness setting so you stay in the sweet spot, so to speak.
Let me clarify that I’m not saying the above types of coilovers are junk, they are all decent pieces. Looking at the design from an objective point of view, they have thier flaws. Unfortunately shock that function ideally are way out of most people’s budgets. Moton, upper end Koni, upper end Bilsteins etc…are proven to be more repeatable, reliable, and linear with respect to adjustability than other brands. Remember your suspension (coilover, sway bars, chassis stiffening bars, bushings, etc) work together as a system. The must compliment each other to achieve ideal neutral handling characteristics