Mine have always turned out good FSU but will experiment FSD. I can see how cap down might be real good on UDS with all that loving goodness dripping down onto the coals then steaming back up to the meat.
I like the thought of the fat protecting the meat too. My last one on the Weber got a little more cooked on the coal side using Minion.
2004 Weber Performer GREEN
Orange Super-Duper Fast
'08 Weber Genesis Gasser
SJG Tamale Pot Mini Smoker (SJG was a rescue)
and a Pyro FIL