line attenuation upped after migration

I was with AOL, and on a 1mbps fixed line,using a netgear dg834 v2. I had a line attenuation of 58 db, and a noise margin of 18db, which dropped over about 8 hours to 11 db. I migrated to BT total broadband today, after the Home Hub went active, ,y line attenuation has risen to 63.5 and the Noise margin is dropped to 5.5 db.
I can understand the noise margin drop with the max product, but why has the line attenuation risen by 5.5 db.
Cheers
Paul

Maybe its now using a broader range of higher frequencies for the higher line rate. Higher frequencies suffer higher attenuation.