so, idk if it translation bug or game bug, but Blessed Vial Pharmacology Book didn't work on heal potions. I check how it works in game and it's need to add 299 var like every level, but it didn't work. If you add something like "15" or "99" to 299 var in something like MTool - it's start working and formula using this levels as intended. I don't have original jap. version due unavalible DLSite in my region so i can't prove my theory.
I'm still looking how Ether Vessel work because i too still didn't find way to upgrade level cap legit without forcing game to have fixed number in MTool (because level check use that var and reverts it).
tldr: add numbers to 299 for heal boost because game didn't do it if even you collect Blessed Vial Pharmacology Book