DHG is more like medium light, maybe even medium-low... but high is okay of course. It's more forgiving than HC, Glosso, and UG for instance.
What's the lighting again? Finnex Planted+ over a 20g Long? If so, then that's more than enough.
Edit:
Take my 6g rimless with a Fugeray-R clip light. It only gets 25 PAR @ 12". I think I'm roughly 11 to 12" from light to sub and my DHG is actually doing well. No CO2 or Glut. My knowledge from before this would have strongly doubted that this was possible. But it is... Still, better light + co2 + ferts will really give DHG the ability to flourish.