Two inches??? Are you putting it on the seat tube or on the chainstay? Chainstay is where it should go.

I've got a couple of Astrales (the Strada predecessor), and I rarely have problems with either sensor, as long as they're lined up. Look carefully at the length of your crank, on the side away from the chain. Mount the sensor and magnet where the crank is closest to the chainstay. There should be a spot where they're within an inch, maybe half an inch. Then it's merely a matter of getting the magnet center to pass over the sensor centerline indicator.