if your extension is wired to the back of the master socket faceplate then by connecting to the test socket you automatically disconnect the extension socket you can check by try phone in extension and you should not get a dial tone
your stats look ok with conenction speed slightly lower than max attainable but noise margin at 7db is gigher than normal 6db and if that reduces then your conenction speed will move nearer attainable speed just needs a stable connection though
Yeah it is connected that way and as you say I don't get a dial tone.
The disconnetions are getting more often now, even direct to faceplate, there have been 4 since my previous post.
Obviously more and more disconnections are going to result in reduced speeds.
There does seem a bit of a pettern with the disconnects, seems stable overnight but from the daytime onwards it gets more unstable.
if you are still using the test socket with a filter, quiet line test is silent, and you are still dropping connection then you need to phone 151 and get engineer visit