I had a guy get Heroic bragging. It was called Heroic Bellowing but that is realy just bagging how your going to kill everyone.
Anyway, I fiddled with him a bit and got it up to Fear +5 before he bought it. No fear magic devices added in just experiance. I thought about going back to a old F+2 save and trying again to see how high it could go but it simpler to ask.
What could I do to boost it? Since almost all the devices are Fear +0 I don't think they would help. The Gift of Kurgi is the only thing I see that he can use and that is a far reach for this game.
I think the Foutain of Blood starts out with Fear (+15), so at least that high.
A Horror Helm will add to existing fear, but the Foutain can't wear one. I don't think if it matters if it's +0 or not, it'll still add something to existing fear.
Put it this way: Ive had a prince of death with fear+30 (he had death10 and a horror helm iirc) so it can atleast go that high. Its a good thing (for my enemies) pretenders cant get heroic abilities (him with heroic cruelty would have been a very bad thing for anything vunerable to morale)