Requiring users to hover to determine the context is a horrible UX. Tooltips/popup descriptions should only be used to provide additional information that isn't required.
It is but an input field is not really an element you would hover for more info. If additional info for the user is required, some question mark icon next to field does the job well because it yells 'hey! something might be confusing or not so obvious'.
I might be an exception but can't recall a case when I would hover input field.