It's always better to do this in the game, if the game supports the sensitivitet you want.
Lowering sensitivity in games does not behave like lowering Windows Pointer Speed. It simply makes the "grid" your mouse snaps to finer and finer.
They all work differently, but making the calculator figure out the 1:1 is something I have planned to do.
For the rest here, as long as the game supports RAW input, uses that and forget about the WPS settings