The lowest I’ve seen a FW 16 achieve myself at idle is 4.5W, but it’s a difficult state to hold for long. That was a measurement recorded on Gentoo.
During regular usage, my 16 sits around 6.5-7W with spikes higher.
My undestanding is the HS is AMD’s middle of the road chip. It’s not the flagship highest performances, it’s not the energy saving U series, but rather a balance of the two.