Whatever settings you decide on, you could always check them on the road, if you can find a stretch with accurate mile markers.

I never thought about a difference between front wheel sensors and rear. How 'bout my trike? I have the sensor mounted on the right side. That wheel will go farther than the left when making left turns. This means that if I ride a loop going counter clockwise I will go further than the other way round. Hmm, I will have to measure the turning radius and calculate the diff. On the other hand, I think I'll just save myself the worry and go riding instead. Mileage is not a measure of effort, it's just a number that needs to be qualified by hard, easy, uphill, downhill, into the wind, etc.