When you think about it, the amount of "settling" of a powder in a powder drop cavity, whether it is an powder measure, a fixed disc cavity or a shotshell loader busing will be greatest on the initial drop followed by a bump. The next bump will have an effect, but it will be less and so on.

If you determine that after 3 bumps or taps or however many, you are not increasing the variation of the dropped powder by a significant amount (determined by you), you are now good to go.

On my Lee PPM, 2 taps is all it takes to keep my variations to +/-0.1g or less so that's the rhythm I use. On my LnL AP with a big flake powder like Green Dot, I return the handle quite forcefully and give a tap to it which causes the powder to settle into the PM cavity to the same consistency.

Some folks use an aquarium pump to put a constant vibration on the powder measure. I know of one reloader who zip tied an adult toy to his powder measure (with pictures) and got great results with 800-X which is a notoriously poor measuring powder.
To each his own.