Levels 1 - 4 take 1 stone per upgrade (so 3 per level).
Levels 5 and 6 take 2 stones per upgrade (6 per level).
Levels 7 and 8 takes 2, 3 and 4 stones (9 per level).
The mod is just a CSV that only edits EquipMtrlSetParam.
INSTALLATION
This mod comes with a '.csv' file, and a 'regulation.bin' file.
The 'regulation.bin' is the actual mod. Place it into your 'mod' folder using ModEngine 2. If you already have a modded regulation.bin, instead use the '.csv' file to merge the changes into it. The relevant params are labeled on the csv files.