Noise Margin And Attenuation ( ADSL )

[OneZ]

Hi,

I have a 256Kbps ADSL connection, my router is SMC.
Statues:
Noise Margin: Upstream 42dB - Downstream 9 dB.
Attenuation:Upstream 40dB - Downstream 38 dB.

Shouldn't the noise margin be a little bit higher and the attenuation be a bit lower ?

My home is about 1KM from the exchange.

By the way, does it make any difference if the link between my router and the line jack in the wall is shorter or longer ? currently it's about 5 meters.

Note: i'm using an SMC filter between the router and the wall jack.

Thanx in advance......