Knitting Needle Size Ratio Question

A bit of an odd question, but I have a pattern that requires a 6mm knitting needle and a 5mm knitting needle, for different stitches within the pattern. Let's say for reasons, I want to increase the larger needle size by 1mm so the larger needle is 7mm. How should I determine what the smaller needle size should now be? Is there a trick to determining that, or some kind of ratio to follow when upsizing different needles? Or, am I overthinking it completely and just need to increase the smaller needle by 1mm as well? Since it's not a 1-to-1 increase in diameter, I'm worried increasing the smaller needle by 1mm won't be enough.