Contact point
The useful mute zone is a narrow strip near the bridge. Move toward the neck and you kill the note. Sit on the bridge and you get almost no mute. Find the spot where a low E or drop-tuned string still has pitch but a short tail.
Pressure and attack
High-gain amps amplify leftover string noise. The mute’s job is to stop unused strings and to clip sustain on the notes you do play when the riff calls for chug. Pick attack should stay consistent; do not “dig in” harder to compensate for a wandering palm.
Downpicking vs alternate
Classic thrash tightness often comes from downpicking because every attack has the same direction and the mute can stay planted. That is endurance work, not a moral requirement. Mixed alternate muting works if the palm does not bounce off the strings on upstrokes.