I have used the inherent hundreds of times and have never seen an echo for an attack using rear legs. Am. I centauring wrong?

The inherent REAR command always uses the forehooves by definition.

From what I see in the helps, HELP CENTAUR states, "Centaurs can naturally rear up to kick with their front hooves."

HELP REAR confirms this with, "While fighting, a centaur can forgo a round of melee attacks to rear up and strike out at their opponent with their forehooves."