It looks like your flame is well below the maximum capable for these burners. Then again, these burners put out way more heat than can be handled by the bottom of a 20" pot. Putting a pot over the burner (with some water in it of course) will give you a better idea of how big of a flame you need. The pot may also change the burner behavior some as well.
Until you get the damper close to 100% open, with a good flame, you haven't hit the orifice limit. So, if you still need a bigger flame, you can keep going. It is a weird interaction of orifice, venturi effect, pressure, gas type, etc., though. Your gas pressure is fixed fairly low, but hopefully has essentially unlimited flow as far as the burner is concerned. I think you may get limited at the high end by the low pressure not creating enough venturi effect. If you still need more heat, you can inject air into the damper to make up for the oxy deficit.
If you really want to see what one of these can do, hook up an adjustable HP reg and a BBQ tank to it.