Here is my take on turkeys and believe me I have done them every way possible.
Cook the bird using the half racks and set it at least 1/4 the way up the basket. Next I found birds larger than 12 lbs need to be cooked with the thighs up near the top or breast side down this gets the dark meat into the hottest part of the chamber.
Remember the "Tommy Ring"? Reason for this was to lift the basket up out of what I called the "Dead Zone" . The "Dead Zone" is cooler and anything cooked there takes much longer. I know the burner ring sits on the lower part of the chamber but the first few inches are not very good for cooking
CharBroil didn't like what I said but they had to agree the upper part of the chamber cooks better than the lowest part (Really heat rises?) Who would have thunk?
Reason CharBroil redesigned the basket with taller legs
Anyway, use your half rack to raise the bird, get those thighs in the upper potion and I bet it will work better for you. If you have questions just ask there are a bunch of great ideas here
Tommy