Purge or not to purge?

I purge when refilling a completely empty lighter, but not when topping off a half-filled one when going out. Recently acquired another lighter with a better fuel window and found that the topping off resulted in little added fuel when not purging.
What's best way to top off a partly filled lighter to get the most fuel into the lighter? Read where chilling the lighter in the frige before topping works - ? True?