Turn off cockpit shaking at high speeds

Isn't it the new "Lock to horizon" slider? -> click

 

I guess that is supposed to do the job, but it still does not.
I have set:
Head Movement 0%
Look to apex 0%
Exaggerate Yaw 0%
Lock to Horizon 100% which imo should lock the horizon completely, right ? It does not. Horizon is relatively "calm" but still jumps, depending on how hard the car is bouncing. I even checked with a piece of tape to be sure I was not imagining things...
I tried Lock to Horizon at 0% and expected a wild bouncing horizon, but that was a lot less than expected.
In short, even with the sliders I can not get the horizon stable (which is what I want).

 

Is it possible to set a little "longitudinal" head movement in AMS? I mean those little "nods" under braking and acceleration. I got used to them in other sims and I miss them a little bit after eliminating the head shaking.