When I mounted my Giessele 1/3 lower third Aimpoint mount it seemed a little short to me. It didn't align with the magnifier. Maybe it is supposed to be like that? If it is, then why does the Daniel Defense 1/3 lower and the LaRue 1/3 mount align with magnifier perfectly? Check out these pictures. Hey, maybe it is supposed to be like that but then the question remains why do the other Aimpoint mounts 1/3 co-witness align with the magnifer perfectly. I figured someone would definitely know here. There are 3 pictures.

You have to dive a little deeper than just a lower 1/3rd description when mixing and matching mounts. You have to look at the actual center line measurement to the rail top.

Trying to find out what the measurements are from the rail to the top of the mount. Has to be somekind of "standard". I didn't know different manufactures would make different heights on an Aimpoint 1/3 co-witness mount. That's why the Giessele's did not work.

There really isn't a standard. Everyone has their own idea what right looks like. The measurement is from the top of the rail to the center of the mount, not the top of the mount. Looks like 1.41 (Doesn't indicate if this pic is co-wit or lower 1/3 but based on the measurement I think its the lower 1/3)