Okay and Happy New Year. DLM likes to see a loop on the line. That's a little simplistic but basically how it works is that a signal is sent down the line and that signal is monitored on the return. If the signal isn't returned or is not as expected then DLM will slow your connection down as it senses a fault on the line that could make it unstable. I know a lot of people do not like leaving their routers on and there is a slight danger in doing so but routers are designed to be left on at all times. I cannot say whether your signal will improve or not but certainly the general advice is to leave your router switched on to prevent DLM from slowing your speed down uneccessarily.
When you do a speed test use this web site. BTW Performance Test
This is the BT speed test website and because BT own all the telephone lines, one way or another, this test tends to be a bit more accurate than the others. Also if you do have a line fault and have to go to BT for help (heaven forbid LOL) they will ask you to do tests from your main phone socket using the test socket that is behind the front face of the main socket and using this speedtest site. Be aware that this website does require Adobe Flash to work.