Had great success tonight, at last.
So my oven has only the one heating element, under the oven compartment, with a metal box below that is the broiler.
I put my HearthKit on the oven floor, with its walls, and on the HearthKit rack I put a cordierite baking stone.
In the broiler I stacked two ceramic baking stones on top of the broiler pan.
I preheated on broil for 1 hr, then baked each pie for 2 minutes on the HearthKit, before moving to the broiler underneath for an additional minute.
Got very nice charring, blistering, leoparding, and overall great texture. I'm going to see if I can reproduce this tomorrow night, but right now I'm very happy. My previous setup involved just using the HeathKit with a baking stone above, and I was getting 6 minute bakes after having the oven on broil for 2 hours.