Codeine Phosphate (C18 H21 NO3). H3PO4 . 1 1/2 H2O mw424
Codeine Sulfate (C18 H21 NO3)2 . H2SO4 . 5H2O mw786

per molecule of codeine base, the phosphate is 8% heavier. Therefore in a mass comparison, the sulfate is a little stronger. If you can accurately cut your pills into 12 parts, you could make up for it.