Have you ever considered whether your horse is more reactive when standing or when moving? It is great to teach your horse to stand still when he is scared…but be sure that when he is moving he is also able to control his emotions.
For lots of horses it is a struggle to keep their emotions under control when they are moving. Meaning the faster they go the more emotional they get. So doing more sacking out when they are standing is good but not the full story. Horses need to control their emotions both when they are standing stil and when they are moving.
Practice reading this horses body launguage. Then re-watch with the sound muted and watch just the horse, then rewatch and watch my body launguage. There is a conversation there even in this shorter video from the Tekonsha series.