Good morning Mr. Buddha Belly BBQ,
Welcome to the Backwoods forum.
First, I think you have some wrong information on the Backwoods Party. You can, I say can, use all the racks in the Party for great food. I have cooked on 10, count em ten grids in the Party cooker for my jerky. The top rack does run a little warmer due to the food being very close to the metal in the top of the cooker but just rotate that grid with one of the lower grids about once in a long low and slow cook or just live with the little higher temp and take the food off a little earlier.
This is 10 racks of jerky in my Party and I never rotated any of the racks during the cook.
A large rib cook in the Backwoods Party. As you can see, I am using the bottom rack in the cooker. I use the bottom rack on most of my cooks. I also use the top rack if I need the space.
Fatboy--the top rack in this cooker (or any upright cooker) will run a little hotter just as with the Party but that doesn't mean you can't use it. And yes, just like the Party, you can cook on the lower rack. As for the top to bottom temps, the Fatboy is a little more even as it has more insulation and has less height in the cooking chamber (ie heat rises.)
A properly loaded Fatboy will have about a 18-20 degree difference between the top and bottom grid and the Party cooker will run up to about 20- 25 degrees. Really not much difference and again, all grids are usable in both cookers.
I hope this answers your questions but if not, ask again and we will try to help.