Lucky for me my two horses are like little tanks, nothing phases them. But a trainer I rode with had three horses that were abosultely nuts.
So I've never tried it first hand but this is what she did and said helped her horses.
put her horses on a Vita B1 crumble supplement. Farnam Co Horse Health 75210 Vita B-1 Crumble 2.5#
At Ease paste(given right before show) At-Ease Equine Calming Supplement - ShanesTack
And Whoa! Calming Agent: Calming Supplements for Horses: Whoa! Calming Agent by Equi-Shine
^Those worked work her horses, but I know of other people who's horses have had no improvemeant with these.
When I was working Dallas who was abused by a harsh traininer as a four year old, no supplements worked. Just a lot of bonding and quite time together until he learned to trut me enough, to know I wasn't going to let anything bad happen to him. I would spend hours groom him, sitting in his pasture reading a book. Talking at him, bring him something nice. And it worked because now Dallas rides and shows like a dream, and has won at shows all around, and I hope to take him to nationals. It was just a lot patience and effort. Even if your horse wasn't abused, a lot of time together and bonding can never hurt. The more trust he has in you the better.
Going out and riding more, as you know, will help too. If groups are his biggest issue, then I would take it slow and work up to them. First by yourself, then maybe add a friend on a quite horse, and so on as he improves.
Never tried or heard of ear poofs. XD But they might be worth a shot.