there's no direct formula between FH skills and tospin (ie: unlike Speed vs Stamina, or Precision vs Power).
However, you hit the ball stronger from power and deeper from consistency, which in turns will modify how the same amount of topspin put into the ball will affect the whole trajectory.
But in short, there's not much reason to change your topspin, except if you're after something extremely specific.
== Mana Games ==
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