I'm right at 1".
But I have to be careful of which way I point my Tunze 6055's.
I change the direction around every once in a while and if I'm not careful, I get water splash over the front edge.
1.25 for me. That is where Planet Aquariums had the overflow Drain pipe set at. Emergency overflow is set 3/4" higher. If you wanted it lower, I would think you could shorten the drain pipe a little. JMO
Just measured mine. Looks like miracles cut the overflow 2 1/4" deep so it runs ~ 2" from the rim with the water level level 1/4" higher than the overflow for skimming. I just trusted them to do what works best and have been happy.