I doubt the hairspring being out of true is affecting your amplitude, unless it has also thrown the beat error way out. If you look at the pic the first thing I would try would be to push the hs in at the green arrow. You can see it is bunched up near the blue arrow and spread out at the orange arrow- this should correct this (mostly) as well as bring the regulating curve more in line. Then you will want to push it one way or the other right at the stud, just a little bit, so that it bounces evenly between the boot and pin.
Hi according to convention when the balance is at rest the terminal curve should rest in the center between the boot and the pin. As you said you should be able to run the regulator arm from + to - without .interfering with the spring If the spring rests on one pin or the other it will affect the swing of balance and the rate Itshould beat evenly between the pins..