We both recognize that both "IP" and "EP" uses relaxation. And both use "ground-path" or the ability to direct something from an appendage/body part to the ground. And they both use good structure, they ability to hold the frame in a relaxed state. So, how is "IP" doing this differently or better then someone trained in an external method?
Really, really, really, really, really overly simplistic response would be that normal/external would be using "beauty" or "gym" muscles where an internal paradigm would be using support muscles to move/support different parts of the body. In the external model, when you 'relax' you introduce a lot of slack, in the internal model you may be relaxed but still recruited/engaged throughout the body.