CHT difference during level flight and descend

Are you measuring the material temperature of CHT or the coolant temperature of CHT (for engines with the new-style heads)? The temperature limits differ depending on what specific measurement you're actually obtaining.

If you observe, cylinder head #2 and cylinder head #3 are positioned differently on the engine—one receives direct airflow, while the other experiences significantly less airflow. This discrepancy in airflow might contribute to the variation in CHT temperature.

Another factor could stem from uneven fuel distribution among cylinders. The intake runners, being of unequal lengths, might result in the front cylinders (#1 and #2) running cooler due to a richer mixture condition.

With that said, Rotax doesn't state a limitation on CHT spread between cylinders. If you are not in an overheated situation and the engine is running and operating without issues, I wouldn't worry about it too much.