Wouldn't Cowardly Horses make horses potentially hard to get back, though? I've never really used horses myself.
Usually they don't run far, in my experience (from a full 3 hour playtime). Als I have found that in combination with Horses for followers... it gets easier to find them (if they run away in a dense forest).
Blizzard Battletag: UnderDog#21677
Shepard: "Wrex! Do we have mawsign?"
Wrex: "Shepard, we have mawsign the likes of which even Reapers have never seen!"