I'd like to create a command which solves ''globally'' the following question: as shown in the picture below, when the glyph ''f'' appears in math-mode, though the horizontal position of the supscripts is cool, the subscipts' one is not.
So, I'd like to use either something as
\ifx\first (et al.) commands or changing the fontdimen's in order to get the horizontal position of the subscript closer to the ''f''.
Notice that the italic correction already applies, and mostly I want to get this result only for the glyph ''f''. ''Globally'' means that I want to get the result when I write e.g.
$f^\ast_\ast$ without other commands. For this latter topic, I saw that in the mtpro2 package a similar solution has been applied for sub and supscripts in general, i.e., globally, but I'm not able to adapt it to the present case.