A guy could write a book on how to seal the deal with an incoming bull....
I think I would respectfully disagree with David. The trouble is bulls will freeze for no reason. If your arm is extended you may be like that for some time. If you weren't shaking before, wait until you have to hold your bow up for three minutes in a stare down.
I hunt with a longbow for elk for this exact reason. I rest my lower limb on my forward knee, standing with my back against a tree,and with my tab hand ready to draw. The long bow is long enough to keep my bow at a respectable height while at rest.
I also tuck my chin and try to look down when they get real close. Those last few yards, I follow the bulls movement with my peripheral vision.
I think,bulls seem to sense at close range when your're googling at them. If they catch your eye, they will grind to a halt, stare, bark, and boogey.
Anyway, I try to have my kill spots in mind and when they walk into them, I swing draw, anchor and release. I try not do this if they are actively looking at me.
Bulls will swap ends like a whitetail if you pick the wrong instant. if you do it right, you will almost smile just before you release, because you know you nailed it.
If you do it wrong, the bull leaving (especially a whopper) will sound like a jeep crashing through the timber. It will awe you with their power. Usually this is followed by dropped bows, quiet f bombs, and other general temper tantrums. Or maybe that is just us.
Anyway, to each their own but that last second or two, I think is the difference between killing bulls, and just telling the story.