Diagnosis
This is due to the natural heat stratification in the unit. The top basket chamber receives slightly less direct heat than the bottom. Using identical settings does not account for this.
How to Fix It
Compensate with temperature or positioning. Method 1: Set the top basket temperature 10-15°F higher than the bottom basket. Method 2: Swap basket positions halfway through the cook cycle. Method 3: Use slightly different cook times. For example, set the top basket for 2-3 minutes longer than the bottom if temperatures are synced.
If That Didn't Work
If the discrepancy is extreme (e.g., bottom burns in 5 minutes), verify the crisper plate is correctly seated at the bottom of each basket. An upside-down or missing plate drastically changes airflow.
Heads Up
This is a characteristic of dual-basket vertical design. You will need to experiment and adjust settings based on what you're cooking. Take notes.