From the 2016 Ram Owner's Manual, you have 4 settings: Light Electric, Heavy Electric, Light Electric over Hydraulic, Heavy Electric over Hydraulic. The Heavy setting is for trailers over 10,000 lbs. There is no medium (at least on my truck there's not). The owner's manual covers the 1500, 2500, and 3500.
I personally use the heavy setting for my toy hauler. It doesn't quite weigh 10,000 lbs, but I can get a better adjustment with that setting. My horse trailer uses light electric. They will lock up using heavy, even at low gain levels.
This is your manual:
http://cdn.dealereprocess.com/cdn/servicemanuals/ram/2016-1500.pdfPage 702 has the info you want.