On BT Wholesale connections. Is Supanet on one, or is it LLU-based?
AAISP also allow 3db noise margin on TallkTalk based ADSL2+ lines:
3dB is now supported! As of November 2015 customers can request a 3dB profile. The process is a little long winded, but once a Support staff member picks up the task 3dB can be applied within a few minutes. Do contact us.