The Netgear is one of those pretty good at hanging on to low SNR lines.
>>> I have suffered several disconnections,
ahhh.. this is when your sync speed will have been dropping which causes the lower IP profile.
>>> it would appear that once your download speed is set, that's it.
Your IP profile from that test is directly linked to your bRAS profile.
Its variable and can change on a daily basis.
If you can maintain a stable higher sync speed for several days then your IP profile will be adjusted accordingly.
Bit more info under the
Data Rate (bRAS profile).
Each time you connect a new sync speed is negotiated.. the speed you sync at will depend on your SNR Margin at that particular time.
It gets a bit complicated but if you try sync in the evenings when your SNR Margin is lower.. then the DLM will always try and achieve a particular margin (say 6dB or 9dB), when it sets your connection speed.
This may result in a lower sync speed - despite the fact that the Netgear is reknown to be able to cope quite happily on 3dB.
If you manage to stay connected for 3 full days at the higher sync speed, then your IP Profile will be uplifted in line with the figures in the table on the bottom of that page.