I definitely think the DLM for my cabinet is very sensitive even a change of SSFP from MK3 to MK2 to is enough to get 3 retrains by the DLM and when the SNRM has hit 4.0dB not one retrain comes in but 2 in under 24 hours so different to other on MDWS
As I said near the start of this thread you gain a lot of knowledge from your own lines behavior over the years but one thing is for certain no two lines behave the same way even if the stats are identical.
I'd find it hard to believe that DLM paid such real-time effort to monitor all lines closely enough to jump in at 4.0dB.
However, the DSLAM can be configured with an SNRM threshold at which a resync will be triggered - this is one of the standard configurable items in the line profile.. I've not heard of this parameter being varied by DLM, but it certainly could be.
If this parameter were set at 4dB for your line, then the DSLAM would drop the sync whenever SNRM dropped to 4dB or less, which matches your experience, but isn't quite the same as DLM monitoring directly.
The threshold can't be set to 4dB for every line - we've seen reports of sync surviving down to 0dB - and IIRC, 0dB is the default.
I could believe that DLM calibrates a line by observing how much the min & max SNRM values change each day, and deciding whether a changed threshold was necessary. It would actually be the first step I'd design if I were asked to implement a DLM that could vary the /target SNRM/ from 6dB to 3, 4 or 5dB. Which, of course, we've heard rumours of...