One small caution with a downstream second stage. When you advance the orifice with the hex key (3/16"), that will indeed seal tighter against the seat and stop your freeflow. But as you do, the poppet carrying the seat is pushed into the reg body and the lever drops. Very small advancements can produce large lever drops. The lower the lever, the smaller the valve can open. The smaller the opening, the less air when you need it most.
That's why with a downstream reg, orifice advancements are ALWAYS accompanied by tightening the lever nut. If taking off the cover and diaphragm and tightening the nut is not something you're comfortable with, I'd recommend that you consult a tech.
If you want to give it a go with minimal risk, try 1/12 to 1/6 turn (5 to 10 min on the clock face) max, and see if it seals up. Anything more than that and you're risking a dangerous loss in air flow from lever drop.
If the pressurized reg "clacks" when you shake it, your lever is loose.