Re:burner distance from bottom of pan??
You can start with the burner manufacture. They should have recommendations for best use practice for their burners. .... What are you doing? .... building your own burner; or buying used burners ... You may have to experiment to find the correct clearance. Check the height of flame when the burner is at high heat. Then set the clearance so the bottom of the pan is in the hot zone of the flame.