Most of it is scattered throughout focusst.org, so I collated it and added missing pieces where I could. It's part of my suspension spreadsheet that I used to design my autocross suspension which incorporates ride quality in addition to static cornering balance.
In stock trim, it understeers a little until the rear swaybar binds and/or the funky square swaybar bushings start oscillating. Tucking into a decreasing radius turn, it will oversteer, particularly if you abruptly lift the throttle, so driving the FoST nimbly is very much all about weight transfer. Swapping out the rear swaybar for slightly stiffer with better endlinks and most of the evil nature of the stock rear swaybar disappears. You can still get a nasty surprise if the rear tires are cold and/or overinflated, but most likely you will never notice such misbehavior on the street. Unless it's wet/slick/steel plate.
To mediate the evil of cold rear tires, I had custom double adjustable Konis made for the front, where I increased compression (aka bump) to slow down nosedive. I also have 0.15-0.2 total rear toe-in so the rears get a little heat via friction. As an autocrosser, the front turn-in felt lazy, so set 0.30-0.35 toe out at that end and that's about at the limit of stability on the highway.
The thing to realize with tripoding is that the rear swaybar is no longer doing anything for cornering balance when the wheel lifts, so our impression of over/understeer is solely based on the few tenths of second before the wheel lifts. As such, the dynamics of inertia, how hard we tossed it into the corner, how much the brakes lowered the nose & reduced roll resistance, and whether we're onto the bump stops from braking influence that impression. Smooth drivers like the stock suspension on that soft rear ST or middle Strano position whereas those who pitch & catch their turns prefer the hard setting. Heavy trailbrakers will tend to say it understeers (because they're on the front bumpstops) and may want more rear bar when all they really need to do is trail off the brakes a bit earlier.
The Eibach rear bar is adjustable. My spreadsheet says when setting it on hard coupled with the Eibach front bar on the stock suspension, you get a mild understeer 0.49%. My preferred ST rear swaybar on soft with the stock suspension & stock front swaybar is moderate oversteer (1.8%) for the brief period before tripoding begins. So hopefully the Eibach springs increase the rear spring rate a bit so drivers have a choice between understeer & oversteer rather than between massive understeer & mild understeer.
