zoomcreep

I bought some Superpan 200 and shot 2 rolls so far. The images without any filter look good but the ones where I used a red 25A filter seem overexposed and lower contrast even when compensating by 3 stops (on the first roll I did an A-B test, one shot with the filter and one without). Both rolls were shot in bright sunny conditions. I developed them in D-76 1+1 for 14 min at 20C. I'm wondering if I should adjust the exposure time or shoot normally and alter the developer time to get more even results.