That just raises the question about how big a human torso would be mounted on a modern horse's torso. A huge clydesdale mare with a typical jockey's torso would look pretty ridiculous. But, maybe a clydesdale-type-centaur would have an Andre-the-giant torso, or maybe something even bigger. Maybe it would be a humanoid torso which, if it had legs, would stand 4m tall.

But, even if it is an Andre the Giant head, imagine how much grass he's going to have to eat to keep his body fed. Andre has a big mouth compared to me, but it's still small compared to a horse.