DIAGNOSIS This is a known thermal dynamics characteristic of this vertical dual-basket design. The top basket is closer to the exhaust vent, creating a stronger convective current and slightly higher effective temperature.
FIX You must implement a manual rotation strategy. Set a timer for the midpoint of the cook cycle. When the timer sounds, pause the unit, swap the basket positions (top to bottom, bottom to top), and resume cooking. For the DZ401, a 5-7 minute rotation for a typical 15-20 minute cook is optimal.
IF THAT DIDN'T WORK Check that you are not overfilling either basket. Overloading, especially the top basket, restricts airflow and causes uneven cooking internally. Never exceed the single-layer capacity guideline. Use the provided measuring cup for foods like fries.
HEADS UP The Match Cook function (not Sync Finish) is designed for this. It copies time and temperature from one basket to the other, but you must still physically rotate the baskets for even results.