All animals are very possessive and paranoid about their food. As long as you are feeding the horse far enough away from the other horse, don't think the feed event is as much of an issue as separation from the other horse buddy. If you keep the distance between the horses several hundred feet, neither should feel threatened or neglected during the feeding event.
As you know, dominant animals will chase lower status animals away from supplemental feed, minerals, etc.
We keep 3 of our horses (gelding 2 yr olds) in same pasture. But, feed them flakes of alfalfa and pelleted feed about 50 to 75 feet apart with no problems. However, they will play "musical feed piles" since they always think other horse is getting the best stuff.
