I have spent the last couple of years trouble shooting this in minute detail. If my line does not disconnect more than eight times a day, the lines people will come out (do f'all) and charge me $180 NZD for the visit.
Now I would like to work out the best SNR for my Draytek Vigor 130. It is not that I am going about this the wrong way (trust me) it's just that I have spent an incredible amount of time and energy on this to date (digging trenches, replacing copper in the ground with new CAT6 in conduit, re-terminating scotch locks that were fine to begin with, replacing wall outlet data mechs, replacing inline ADSL filters, substitute router, different router firmware versions, putting my router out at the demarc blah blah blah). From here I guess that the only thing to do is change my VDSL delta value by increments of 5 every 48 hours and try to work out (somehow) which value is best. After a few weeks I should have an idea. I will let you all know how I get on as it may assist someone else either now or in the future. Thanks