You need a carbon layer, but a no-cake thin layer will do. When you don't have to ream, the bowl doesn't take that damage, peeling off a little briar with the cooked on ash, and also the stress of reaming on the bowl. Also, this maintains the full capacity of the bowl, which is useful with any blend, to give it full room to unfold. I'm making my case for the way I do it, and if I liked a good thick layer of cake, I'd argue for that. Do what pleases, first. This is what pleases me.