Here's an extreme high-tech one I came up with specifically for shooting with irons and unmagnified red dots out to 100 yds and beyond. I can shoot great groups with it because I use the angles to establish a tangent with the dot/bead.
I forgot to add that I need to compensate for shooting for where you'd normally place the dot/bead--in other words if you place the POA on top of the dot/bead.