Unfortunately we have no idea how to fine-tune alchemy. There is (I think) something like a GMST for the general power of player-mode potions, but we can't control the powers of the particular effects (the magnitudes have no effect in game). At the moment, player-made shield potions are way too strong, and player-made health potions are way too weak (just to name two examples). If we vary the GMST, either of these problems may be solved, but the other one will worsen.