I'm not the best shot in the world, but you can use a 6 o'clock hold with a bead accurately on a target providing you have a good steady position and the right type of target (eg white background with a black circular centre), but that comes undone in less stable positions or for quick shots where you tend to centre the bead and therefore go high.

I find a 6 o'clock hold with a bead is not too far removed from the military Mauser front "spire" blade, and I guess this is where my habit developed from.