Sorry typo
3mm high and ~12mm long
Careful filing and sanding then scouring pad gives a reasonable finish. If you want a mirror finish with no sign of tabs then you are back to fixing the part down in the middle using any holes that are available instead of using tabs.

On occasion I've also put the raw tabbed part in a vice edge up and used the machine to skim it down 0.05mm at a time and remove the last but if the tab. You can get a very good finish but you ideally need a parallel edge on the lower side to reference to sitting in the vice. But this takes time and is best for simple shapes.