The Horn needs to be moved to level 3. If you nerf his current Horn stats, it'll reduce his overall usefulness to the point where nobody will recruit him.
Look, the biggest threat to Boro is fear-resistance. Moving horn to lvl3 has the highest probability of making the power useless because people will have longer to get fear resist.
Forward statue camp already makes horn ineffective. Mordor has easy fear resist from Gothmog.
Reducing the range is better IMO, because you just increase the micro a bit and prevents Boro from freezing armies that are split up.
Side note: I hate the fear mechanic. It's so dumb and obvious. "Oh my opponent has fear ability, so I get fear resist". Especially because some factions have waaaay easier access than others.
Smokk - Mordor