Usually there is a grease pan between grill and source of heat.
It works somewhat in vertical cabinet smoker. But the upper grills will drop grease to lower grills.
If you place grease pan under each grill, it will effect hot air/smoke circulation.
In pellet grill like Traeger, there is a grease pan between fire pot and grill. the Grease pan effects hot air /smoke circulation too.
In traditional BBQ, grill is direct above the charcoal fire . Grease drops to charcoal and gets fire/smoke to effect flavor of meat.
With my design of composite grill, grease is collected before it drops to lower grill or charcoal fire, meanwhile hot air/smoke can goes freely through gaps between each grill rod/bar/arc.
Do you like this design