Does one of them wear glasses?
I can't wear my glasses when shooting because it changes the point of aim.
I didn't wear glasses when I started shooting, so everything is set up for my naked eye. When I started wearing glasses I tried shooting with them. I expected to see some difference, e.g. maybe the ranges would be different or something, but was surprised that the aim changes significantly depending on which way I tilt my head. I found it would change in both elevation and windage, just by tilting my head a couple of degrees more.
I decided at that point never to wear them whilst shooting. I miss enough targets on my own as it is, I dont need that kind of variability. I would bet it must affect people who shoot in glasses when they come across a target on an incline or non-flat ground. Or any other condition that made them shoot in a position slightly different to their sitting norm.