Follow the numbers - number will guide good QA decision making.
You did not mention requirements reviews or design reviews, or any other QA steps. Have these been done? The numbers show these QA steps are more effective (several times more effective) than "software testing". It does not matter what stage you are at, even if you have the code done, do these steps before you do "software testing". (This is the advice Tom Gilb gives, and having been there and done that, I would agree with him).