The name high-pass filter describes which side of the spectrum passes more freely. Its cutoff should not be read as a border below which every sound instantly disappears.
Read cutoff and slope together
The Audacity high-pass guide explains that frequencies below the cutoff are progressively attenuated. The roll-off setting controls the steepness of that reduction. Moving the cutoff and changing the slope are therefore different adjustments.
On a practice copy, listen to a short passage containing the unwanted low sound and the voice you want to preserve. Make a modest change and compare the same passage again.
Listen for the cost of the change
A setting can reduce unwanted material while also changing the desired voice. Describe both results. If the voice becomes unhelpfully thin, stronger filtering is not automatically the next step.
Save the settings beside the recording’s specific problem instead of labelling them a rule for every microphone. This makes the experiment repeatable and keeps the tool connected to an audible purpose. A filter is easier to use thoughtfully when its curve is understood as a gradual response rather than a perfect separator of wanted and unwanted sound.