As soon as trying to extract the most performance out of a wing is attempted, you will find even small changes can produce large effects. I'm not an aerodynamicist but had to reprogram the Stall Protection Computer on a Regional Jet after the wing was found to have less than optimum performance. I eventually filled a whole filing cabinet with change documentation & bench test results before the final solution was found by our Flight Sciences group - and that was without making any major changes to the airfoil or planform!