Thank you again for those explainations. Not that simple ...

I have the oem sway bars, and my car is MY2002.
I found this on s2ki:

Summary of spring rate findings:

Front Rear Front Rear
Model Year Spring Spring Sway Bar Sway Bar
--------------+------------------+--------------------
2000-2001 219 291 393 427
2002-2003 246 309 300 396
2004-2005 262 278 300 311
2006-2007 262 269 300 311
2008-2009 280 294 354 311
2008-2009 CR 384 343 392 362

Maybe softer rear sway bar

And get 15mm rear preload..

I had no problem with my previous coilovers, so I will start by changing the rear Ohlins coilover preload to 15mm !
Maybe I will get Eibach swaybars (or else) in the future if necessary, I will see on track with the supercharger...

Thank you all for your help adn explainations, because over than the solution: I like to understand things.

Now my goal is: change the rear preload and re-adjust the height, in order to keep my alignment settings (brand new: done 1 week ago !)...
But it will be impossible to be sure, so I will pay again to check alignment I guess...

Examples on bias from one of our residents
https://www.s2ki.com/forums/s2000-br...1183541/page3/

Measure wheel from arch first ,then preload adjust, so counter adjust with perch adjustments.……..
then no need to pay again.

This is what I will do, but it is hard to get back to the exact same height. Even if I move my car in my garage, my heights change at the four wheels ! (only a few mm of course, but it is not easy to fix something in this situation...)

Only a few mm lower or higher wont change the toe angle much at all.
By the way did you have the exact same alignment figures with the Öhlins as your previous coilovers?
Show us the setup if you got a printout, maybe there is something that could be improved there as well.

This might sound stupid but, did you check the adjustment knobs to make sure they are on the softer settings? Also, I would maybe take the car to a different shop and re-check the alignment?

Add 13mm of preload (use turns, not measurement). Each 360 deg turn of the perch is 1.5mm.

Then lower the bottom bracket by 13mm to keep the same height.

Easy peasy.