With a 6dB SNRm, its unlikely anything can be done to improve the situation, You've probably just become a victim of crosstalk like a lot of us have.
I used to have 100Mbit on Digital Region with an attainable in excess of 130Mbit, then once on BTW with Zen 80Mbit, then down to 66Mbit, thanks to crosstalk.
My line is shorter than yours with Line Attenuation 13.2dB down and 16.3dB up. I can't see how backhaul has anything to do with your problem, that would be if you were getting much slower throughput compared to your sync rate.