Look at the picture of the upside down clump. For me, the storage roots are the larger tubers and the feeder roots are the thinner roots attached to them. Some can be tiny and reach out two feet or so away from the main clump. I always use water pressure to remove the soil from around the tubers and flush out the smaller feeder roots. I don't know if this really makes a difference but it sounds logical to me. The vendors usually trim the roots for packaging and shipping reasons.

Okay I see. When you say you use water pressure to remove soil, I assume that is after they are dug up and you are trying to get the impacted soil out of the clump so it doesn't hold moisture that might cause rot over winter??

Try checking this post from last year. It explains the procedure. The thread "Digging and dividing a fern leaf peony" in Peonies forum

Will do. Thank you.
Mary

Checking out Jerry's previous post about fern leafs. Good drainage and sand. Got it.