@addicted-to-smoke. I tried to duplicate your set up for tonight's cook. I used two baskets, opposite sides, about 3/4 full. I ran a digi probe up through the bottom vents sitting about an inch off the cooking grate. Also, there was a aluminum foil pan between the baskets.
I left the top vents fully opened for the first 30 minutes. The dome temp ran at 360-370 while the grate ran at 375. Very close.
I tweaked the top damper about 30 minutes in. It was reading 385, while the dome continued around 360.
For the next hour and after refueling, the temps continued to run 20 to 30 degrees apart with the dome being cooler.
Now, I was cooking on a newer performer. This is where I wonder if we differ. The temp gauge was in-between the baskets, but the vent was over one of the baskets. Dont know how much that would effect it, but I'm sure it would some.
Anyways, it was a fun experiment.