Are you using the 9.1.6 or 7.1.4 test tone from Dolby by any chance? If so that is known to be a bit bugged and running about 10db too high on the subwoofer. The more accurate one is the 5.1.4 tones.
I feel when it comes to subwoofer levels you are best setting it to your personal preference and room acoustics. Even with the 5.1.4 tone mentioned above, my meter had me putting it in the +3 to +6 range which to my ears is too overwhelming and bought attention to itself so it didn't sound well integrated.
You will often find people recommend listening to music and set it where you just hear the bass start to get filled in nicely (aka the 'by ear' method). Mine is set to -5 and I feel that it is well integrated. As mentioned it's really personal choice though.
Best of luck.