It's a 20 qt, fired by the Bayou Classic SP10 burner I keep the lid on as much as possible, but, yes, I think that you may be right about the lead getting bound up in the slush.
I am going to reheat the pot, skim the remaining dross, flux again, then cast ingots. I will then attempt to remelt dross, in smaller quantities, using charcoal in the mix , keep it covered and see what happens. The lead should drop out!
I'll make pix and post them.
Good thinking about thew slush layer, although the pot did hit 780ºf (ouch), it is a possibility.