As for the fattie or ABTs I would go above and off to the side a bit, mostly for presentation than any other reason. Too much drippings may discolor the turkey, but then it may add a really good flavor
If you are using a thermometer on the rack next to the bird it wouldn't matter which rack you use. I think most of us put poultry below other stuff in the smoker or use a pan below the poultry to catch the drippings.
Remember they recommend not low and slow smoking a turkey larger than 12 lbs so if you want more turkey just buy a couple 12 lb'ers