You should tighten your elements no more than 8-9 full rotations. This is to protect the screen within the filter that contains the fluoride and arsenic reduction media. If you can tighten the Fluoride and Arsenic Filter all the way up the stem for the Black Berkey® Elements, Super Sterasyl Ceramic Elements, or Berkey Earth® Elements without reaching 8-9 rotations, that is perfectly fine.
The most important thing is that you do not overtighten the elements, which may cause damage to the inner screen of the elements.