Interesting observation, thanks! I hadn’t thought about it. The experiments were all done while connected to the charger, so that would be on USBC power.
I didn’t capture the EPP, but having looked at it now it appears the EPP hint on my system is always performance, irrespective of PPD profile and AC power. That is assuming /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference is to be trusted. I’m inclined to believe this was also the case for when I ran the experiments as nothing much has changed since (other than a kernel update from 6.6.21 to 6.6.30).
Can you please clarify where you get the EPP hint from if different from above? There may be differences in behaviour between distros and/or kernel versions. AMD keep making updates to the amd_pstate driver (which is good) and I only run the “longerm” line of kernel releases - this is the default on Gentoo and I CBA to compile a new kernel every time it pops up. So not sure if any of the newer changes have been back-ported to the longterm 6.6.x line.
There’s a pretty good thread on tuning fan behaviour with ectool here. I did not link to it earlier as the original post is for the Intel series of the FW13, but there’s a good degree of overlap and has a lot of useful information on the matter.