As SNRm per-band is almost ~6db I would think that line condition is perfect as it is, from:
I am in a rural area and the best BT and a smarthub could get was around 30-33Mbps and now I get a little over.
I think may be it is Copper from exchange to the PCB then Aluminium from PCB to homes if BT was keeping cost effective/performance equation in mind (but this is my speculation) now that there is an FTTC cabinet probably near to the PCB one that would be an Aluminium role to keep speed low.. also as I can imagine the cabinet is at the beginning of the rural area then lines going from that point so that could be a considerable distance + Aluminium
When you say "The SNRM values are around 6dB which is the usual default value" does it stay at the default value if you change the current value in Administration - DSL Settings - Stability Adjustment. What is the purpose of this of this adjustment?
Sorry to ask simple questions.....
No worries about questions
sure SNRm 6db is the default profile since FTTC started that is almost all over the world like a standard profile, DLM could decide to raise it if the there is a line fault or faulty modem or a big source of interference affecting the frequency of VDSL2 in a band(s), yet OR pushed the 3db as the company decided to make the lines capable of delivering more speed but that is controlled by DLM and for certain lines that are able to keep the service running at 3db with certain standards [like errors below certain level, not exceeding a max. value of ES (error second) etc.] and also available on Huawei cabinets only as I believe..
For your question "What is the purpose of this of this adjustment?" first of all mediatek and lantiq chipsets (and if the manufacturer allows it, ASUS allows it from UI, others from ssh/telnet commands, others may disable such things like ISP provided ones
and the cabinet accepts such adjustment ) are the only ones as I remember that can force an adjustment for the SNRm value and usually for the purpose of getting more speed from the line, like making the SNRm 3db but that may affect service stability so it is by trial and error to find the value that any decrease after it and the line will not be stable,, but if it is available or not other kitzens may provide more info. since I did not try anything like that before.