MotoIQ's Mike Kojima got a chance to look under the Greddy car and critique the suspension setup. Some interesting quotes from it:
The FR-S [front] suspension is conventional MacPherson strut. The Greddy car had a prototype set of Greddy coilovers. The only adjustment in the front alignment is the toe which is typical. No provision for camber or caster adjustment is present on the stock car, at least this stock prototype! The front suspension has a good amount of caster, king pin inclination and trail which is good for camber gain under cornering, straight line stability, good on center feel and good self aligning torque with minimal scrub. These aspects of the front end geometry are reminiscent of the Nissan S Chassis and older BMW's, good things.
...due to the angularity of the lower arm when lowered, the front suspension will lose negative camber under roll which will reduce grip and even lead to understeer in a low car unless a lot of static negative camber is dialed in or roll is greatly reduced with stiff suspension. Big negative camber hurts braking traction and causes the car to be road crown sensitive and tramline on cracks and grooves. Being too stiff hurts mechanical grip. Whiteline if you are reading this, this car really needs your long shank ball joints and tie rod ends to correct the roll center. Make some right away please. Maybe your Subaru kit might fit. The best solution before the aftermarket responds might be to not lower the car more than 1.5” or so.
Lowering most cars beyond 1.25" means you're going to start adversely affecting handling unless you make other mods.
A basic rule is that once the lower ball joint is higher than the lower control arm mounting point, you're outside of the suspensions proper geometry. That's not always the case, though. And there's modifications that can be done to make this "rule" obsolete.
Pretty common for most cars to not handle as well when lowered too much, irrelevant of the set of coilovers being used. I remember back in the day when best motoring was reviewing the DC5-R and they actually said the optimum height for the best handling was around where honda designed the car to be at with the stock suspension. As much as I hate to admit, my tC probably doesn't handle as well as it can because I'm lowered over 1.5"...the ride isn't compliant enough and I do feel the understeer when cornering hard