There's a dozen reasons why the SNRM doesn't run to target.
The fact your line jumped straight from 6dB to 3dB in itself shows it isn't the DLM setting that target.
There's probably over 100 instances on this forum of ECI lines appearing to be on 3dB that weren't, including lines that resyncs at 3dB.
There have been threads that were many pages long with dozens of examples of lines at 3dB and not a single 1 of them was a target set by the DLM.
OpenReach have confirmed numerous times over the years that ECI lines haven't been part of any 3dB trials or the full rollout yet examples always pop up.
The ECI G.INP trial has hit another issue.
If they were going to trial lower dB targets on ECI cabinets it would need briefed to CP's.
They need kept in the loop on fundamentals like that.
Every stage of the Huawei dB trials was communicated to CP's in advance.
There has been no such briefings.
If it ever does come to ECI cabinets it will be briefed.
It will follow the Huawei dB process by moving in 1dB increments.
It makes no sense to try lower dB SNRM targets without working G.INP.
It makes less sense to jump straight to 3dB, the lowest possible target, without ever having even tried 5dB or 4dB.