My answer may be a bit different from the other person's response. I do agree, however, that if his behavior IS out of dominance, you need to do less sooner rather then more later to correct the behavior. But you need to make ABSOLUTE SURE that his behavior IS NOT out of FEAR or UNCONFIDENCE. Sometimes people get fear/unconfidence mixed up with dominance just because they don't know what to look for. You need to pay attention to body tension, if he's blinking a lot or not, if his ears or tail are tense (feel them), if his head is a little high, etc. Sometimes horses will crowd you when they are afraid, it's herd instinct. And when the person acts like a predator, it can make the horse feel defensive and pin their ears, try to kick, bite, etc. but it's all out of fear/unconfidence.
I let my horse rub on me, lick my hand (if he's polite), snuggle up to me, and a lot of people would say that is "disrespectful" behavior. THIS IS A TWO WAY STREET RELATIONSHIP. If the horse gives to me, then I give to him, and if that means letting him scratch his head on me, then I'm fine with that. Now of course, sometimes it may get a little rough, but I simply say, "Ok, too rough, please back up" and my horse respects that. Then I'll scratch his head with my hands.
So really, watch his body language. When you correct the behavior, don't be aggressive, loud, etc. about it. Alpha horses DO NOT get emotional when correcting another horse, so neither should you. You shouldn't smack, jerk, yell, growl, or in any way get aggressive because that will only make him not like you. You SHOULD be assertive and get your point across. Like when a horse pins his ears at me out of dominance, I back them up until the look on their face changes to soft. But I don't yell. I'm very calm in my emotions but I have a lot of energy in my body.
I would also suggest considering doing the Parelli 7 Games with him. That will help you a lot with this issue.