Aussie, I did the cook in the 16 inch and it is pretty close to the lump, maybe 2 inches or so but I did have the basket full.
@ mk1, the thing I noticed most is that the meat seems to be continually basted by the meat juices or perhaps you mean why run a rotisserie this way, I'm pretty certain you could get a lot more meat on using this method especially if you were using a larger grill. I was using the 16 inch.