Jim, I've done them both ways. I don't think that it really matters. There is so much internal fat in a butt that the direction of the fat on the outside really doesn't have much of an effect on anything, at least, from my experience.
Jim Warren,
I agree with Jim Clay. It doesn't make a difference. In fact I remove the fat cap to get more bark. I've never had a problem with a butt drying out.
