It doesn't matter.
I use absolute co-witness simply because I leave the rear sight down and want the exact same cheek weld shooting the red dot that I use with my irons.
The important thing to remember is that the irons and red dot are separate sighting systems, use one or the other, but don't waste any time lining the red dot up on top of the front sight post. It's not needed, the dot is where the bullet is going to hit............... period.
For precision work with a red dot turn the illumination down so you can barely see the dot. This allows for the smallest possible aiming dot. Pay attention to the target, not the dot. The dot will be visible without looking directly at it.
Red dots are the fastest short range shooting system currently available. The main reason (US Armed Forces) use lower 1/3 is so the rear sight can stay up and ready for use. If the red dot dies in the middle of a fire fight they can immediately transition to the irons. No time is wasted flipping the rear sight up.
1.5" centerline height is the nominal absolute co-witness height, lower 1/3 places the dot approximately 1.65" above the rail. The difference is relatively small.