None of the above. I put it in a pan raised on a grate inside the pan, just like if I was roasting it in an oven, and cook it until it's done. OK, maybe that is horizontal, but I'm thining what I just described isn't what you meant by "horizontal".
I save the pan drippings for gravy or for adding for extra flavor to broth/stock that I make from the leftover carcass. I usually get a couple meals at least, maybe 3 since most times I cook two birds at a time. The first night we eat the smoke-roasted chicken, maybe with some mashed potatoes and chicken gravy, and make pot pies with leftover chicken meat and gravy, for example. Love it.
I used to do it using some of the various methods above, but I find it is just as good this way, and I can get a lot more out of it. Just my 2 cents.