Did you know that if you do lower 10th co-witness… you can still confirm position of your dot on the irons.
It doesn’t have to be in the center of the window.
What @Clusterfrack is doing differently here is having irons that don’t actually place with the dot.
The irons are designed to be “off” but aligned when holding in a traditional dot index (that would put the front sight higher than the notch in a lower 10th co-witness).
This is a schematic.
So again that “well known trainer” doesn’t seem to be giving good advice. You can check your dot to irons even with a lower 10th co-witness.
Doesn’t have to be in the middle of the window.