My newish paint gelding has the same problem and I think in his case its learned behaviour (its keeps people away from him) mixed in with a lack of respect. We are working on both, i need him to know people are a good thing, then that he should respect them.... But what I am finding that is helping him to come around are treats.. I know I know... they can be over used, but in this case when he sees me he knows its always always good news. And when we are doing ground work and he respects me and lets me do what I want with out a fuss he gets a treat. DO NOT OVER TREAT! Treats can be used to bring a horse around to something new, and at the end of a exercise, but not ever other second.
I have never done clicker training, but have a friend who swears by it for her aggress/pissy lipozzaner mare. She charges the clicker with treats (this only ever needs to be done once) ie.. CLICK then treat, CLICK then treat, CLICK then treat, do this about 15 times then the horse will get that "noise = treat". Then you could spent some time with her, anytime her ears come forward click then treat. If it is a learned habit, you could help her unlearn it. I have never done this, but I was told it works wonders.