Such side to side, front to back, and top to bottom differences in temperature are common in many types of cookers (even your kitchen oven). As long as you understand the differences (as you now do), you can take advantage of those differences. For example, small pieces of meat cook faster than larger pieces. Put the large pieces in the hotter spots and the smaller pieces in the cooler spots. However, if the pieces have different fat content, the one with more fat will cook more quickly.
A packer brisket is a large piece of meat that consists of two different muscles. The flat contains more intramuscular fat so it cooks more quickly than the point, which has more connective tissue that takes longer to break down. Thus, you want to place your brisket into the grill chamber such that the point is towards the end with the higher temperature and the flat is towards the cooler end.
I also have the Ironwood 885. When cooking multiple pieces of meat like several chicken breasts, I will monitor the temperatures of each piece half way through the cook and swap positions of the pieces with the higher and lower internal temperatures so they all finish at similar times. The more cooks you do, the better you will understand your particular grill and the better able you will be able to achieve the results you are looking for.
If you go back more than 100 years ago, cooking was done on open fires and cast iron cook stoves. They were not nearly as sophisticated as your Ironwood, yet home cooks still managed to prepare some great meals. It is as much art as it is science.
