It is not about the size. The judges could care less how big or small the horse is. What happens is that a large horse will look different in the way it mores. It will be harder to see the definition of speed in the circles and the turns will not look as fast even though the horse maybe doing things as the same speed the size will make it look different.
-I'm so busy... I don't know if I found a rope or lost my horse.
-An Armed Man is a Citizen an unarmed man is a subject.
-Where ever free speech is stifled Tyranny will reign.