I think more HF/DM ratios would be useful.
When making areas from scratch in L3DT I use 128 HF/DM ratio. If I use higher values, I find the terrain has more peaks and depressions than I need. I use low values of noise too for the same reason. So, I usually can't compensate for lower HF/DM with lower noise.
Also, if you want to generate a simpler map, such as a river valley flanked by hgh elevation, higher HF/DM ratio is better.
It's better for editing on the DM too, at least if you suck at brushing like I do.
Higher HF/DM speeds up processing too.
When importing a height map as a DM the reverse problem occurs. The height map is high resolution compared to a L3DT generated DM so even a low HF/DM ratio produces a larger L3DT height field than one needs.
So, HF/DM ratios of 1, 2, 4, 8, 256, 512, 1024, etc. would be useful.