Physics was never my strong point. Thanks for the explanations.

I had noticed a slight increase in sync speeds & SNRM (FTTC) as the weather became colder.

I have hung on to an almost 30Mb sync speed, but my DS SNRM is currently down to 2.7dB.
I expect the connection to re-sync (probably at a much lower speed) if this warmer weather keeps up much longer.