We had a couple of advanced BL'ers awhile back who had issues with the usual CWE process for Ibuprofen. The problem being that in it's ionized form it has very little solubility but when added to neutral water + pill excipients a portion can change to the non-ionized form which has much higher water solubility . When it's pKa is taken into account, the pH of the cold water would have to be very low to keep the Ibuprofen's solubility low.
The solution is to use lemon juice in your cold water, enough to substantially lower the pH so upwards of 25 % lemon juice to water. The low pH won't effect the codeine but will allow less Ibuprofen into the final solution.