Constrain delay compensation (don't get it)


I thought I understood this in N11 but in N12 i can’t get it right.
I have midi tracks delay set at -400ms to play MSS (kontakt).
but when I activate or not the Constrain Delay Compensation (call it CDC) in N12 Midi notes sounds with the same offset. Is there something I do wrong ?

In N11 I use to playback without CDC to hear the midi track correctly but I would activate it to record next midi event so I would not experiment delay while recording. I remember it working (although I don’t explain it very well)
Is there something I do wrong ? a setting somewhere ?