[Suggestion] Mounts
Horses and other mounts shouldn't make a champion or sovereign immune to being knocked prone, in fact it should be the exact opposite. Getting knocked from your horse it's very unlikely you are going to be able to land on your feet. Extra movement is bonus enough imho, you could add a charge and initiative bonuses to make up for the increased chance of being knocked prone. Additionally if you are knocked prone you might lose a turn getting back on your mount or just be reduced to whatever your base movement rate was without a mount.