I guess it depends on what you are trying to do. I would only cut the main plant like that if I was going to lose it due to weather, or if the shape on it was terrible...really straggly, or very tall with growth only on the top.
Are these plants in the ground or a pot? Greenhouse? I know you are very far up north, so you would have to dig them up at the end of every season if you had them in the ground? I feel very comfortable that your root ball would re-grow if it was in the ground or established for a few years....could you post a pic of the one that is 4ft high with the thick trunk...I would like to see it. Do you just take a lot of cuttings from it?
Thanks Ken
Terry
