To take measurements, I bypassed the pressure limiter of the rear circuit and I bled, bled, bled....., the pressures should therefore be the same in front and behind but this is not the case , the rear pressure is a little lower than that of the front. I did a test at low speed, the front wheels locked but not the rear ones.
And I still don't know where the extra fluid that comes out of the master cylinder goes when the stroke lengthens under the effect of the brake booster. I have braided stainless steel hoses everywhere and the only explanation would be that the calipers spread under pressure, I had this on a motorcycle from the 80s, it braked well but the handle was not hard because the stirrups of the time lacked rigidity.