I have around 20-23fL and I find HDR with DTM is amazing. SDR targets around 16fL for the max, and even lower for the "normal" content, so it doesn't take a lot of brightness to make the regular parts of your image look plenty bright, and that leaves a lot of brightness for the highlights.Hi. It's more like 26FL in low lamp, but since DTM has to actively dim the image to extract the proper highlights, that number can go down significantly depending on content.
Your NX9's lens/the additional brightness may be saving the day there.
With DTM, I think you can have HDR that is "better than SDR" around 18-22 fL where you needed around 30fL on the old static tone maps a year ago. You may not get eye searing highlights, but do you really need it to hurt to look good?