I dont care what the distance is from the exchange and I understand that I will not achieve anywhere near 8 meg let alone 20 meg!
What I do expect however is that the max speed that is available should be consistent. Full stop.
I can live with a 256kbps upload or whatever. But thats where it should stay.
If it can,t stabilise at any particular given speed, then you aren't getting what you are paying for at all.
If they can't achieve that, then technically how can you claim broadband is actually available?
Remember, the download is always pretty stable, so why isn't the upload?
In broadband terms "up to" is a pseudonym for "we don't care".