Usually when people use that term, their gun shoots too flat and they raise or build up the comb for a higher POI. It matters not whether they see the barrel or bead as a reference while making the bird/bead/barrel intersect with a moving target to break it.
I like to set up my gun with about 60/40 poi with stacked beads. Then I move comb up to about so the gun shoots 80/20poi. This means I am seeing a lot of rib between beads. Thus I am shooting off the front bead--end of barrel.
I blackout my mid bead --I don't want to see it. i think this helps get your head up off the receiver for a better view of the target. I am a one eye shooter and getting my eye high off the receiver is very important to me...SMOKIT
Smokit gave a very good explanation.. well to me at least... Basically.. all you see is the end of the barrel.. nothing else exist in your barrel picture... Then there is the relationship of the end of the barrel.. to the target..that becomes your memory bank of picture.. hit... It's a finite relationship.. that's done from the subconcious.. When done correctly.. results are normally very good.. It does require much practice to master it..as no thought is involved..
When the target appears I lock on the target with my eyes. When I swing the gun to the target I see the end of the gun as a shadow. As the shadow passes the target I pull the trigger.
In this game the vision needs to be on the target. To see anything else(the bead)clearly means I have to look at it. If I look at it I am taking my eyes off the target. A definite No-No since I can't focus on more than one think at a time. I keep my focus on the target. At least that is the plan.