yeah on the St Croix you have to fill the gap on the stove adapter prior to putting it on stove. With the Harman, the interior pipe liner goes inside the stove tail piece and the outer part of pipe goes over stove tail piece. So the stove tail piece is in the gap between inner and outer pipeI too came from wood stoves and loved the look of the Hastings, and it ran great. It just had some things that I preferred not to deal with (the biggest being the hopper size, many times I cam home and it had run out of pellets in 13 hours).
Glad I was able to give real-life experience and helpful information. Having that adjustable piece certainly makes the switch easier.