10 Training perdiod working properly with ADSL2?

[#1]

Finally took the plunge and was regraded to ADSL2 on Monday from a fixed 2mbit connection.
pre regrade my SNR was 12-15 due to line issues, because of this I wanted stable over fast but never had less than the 2mbit so didn't worry about it. So Monday came and my router synced at 4000ish and initially my Profile was 8000 with a SNR of 8-10, IP profile dropped to 3500 or there about after a few disconnections.  What I don't under stand is why with a few disconnections at peek times my SNR drops but doesn't increase.
Until my last lost sync my SNR was 5.5 too 7 when I was expecting 10 too 12 and now its dropped again to 2.5 too 3.5.
I have a long line that was border line in getting 2mbit as it was, so why is my SNR dropping when i have had peek time disconnections?
router Draytek Vigor 2800
Firmware last they ever released E.38.2.23 for it

[#2]

The WBC 21CN ADSL2+ service is rate adaptive where the sync speed is set by a 'target noise margin' rather than the fixed speed you are used to. The target noise margin is set by the exchange equipment to provide a stable service, in the range 3-18 dB in 3 dB steps. The initial value is usually 6 dB. During the training period the DLM at the exchange chooses a target noise margin appropriate for your line with disconnections resulting if it tries a different setting.
Kitz provides an excellent description of how 20CN maxDSL works here. 21CN difference are covered on her navigation menu too.

[#3]

Hi Gus,
I can have the target set at 6 tomorrow if you think that may increase the stability.
Jojo

[#4]

I'll wait out the 10 days give the system a chance. If it fails to chose the right one or more likely when it fails, I'll bug you to set it a bit higher Jo.  Currently the SNR is  averaging 5.5 too 7.