MTU bloccata a 1470

[totolac]

Ho appena avuto la linea Tiscali 4 mega ho questi parametri

linea 4096/512
occupazione capacità (%) down 49 up 65
margine rumore (dB) down 25.50 up 20.00
attenuazione (dB) down 21.50 up 13.00
potenza in uscita (dBm) down 20.00 up 12.00

speedguide mi da questo:

MTU = 1470
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput. If you are using a router, it could be limiting your MTU regardless of Registry settings.

MSS = 1430
Maximum useful data in each packet = 1430, which equals MSS.

Default TCP Receive Window (RWIN) = 251680
RWIN Scaling (RFC1323) = 2 bits (scale factor of 4)
Unscaled TCP Receive Window = 62920

RWIN is a multiple of MSS
Other RWIN values that might work well with your current MTU/MSS:
503360 (MSS x 44 * scale factor of 8)
251680 (MSS x 44 * scale factor of 4) <-- current value
125840 (MSS x 44 * scale factor of 2)
62920 (MSS x 44)

bandwidth * delay product (Note this is not a speed test):

Your TCP Window limits you to: 10067.2 kbps (1258.4 KBytes/s) @ 200ms
Your TCP Window limits you to: 4026.88 kbps (503.36 KBytes/s) @ 500ms

MTU Discovery (RFC1191) = ON

Time to live left = 57 hops
TTL value is ok.

Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = ON
IP type of service field (RFC1349) = 00000000 (0)

ho impostato l'MTU con DRTCP a 1500 ho riavviato e mi ritrovo sempre 1470 di MTU; anche le chiavi di registro presentano un MTU a 1500 quindi adesso non capisco che devo fa? mi dareste un consiglio per favore?
ciao e grazie in anticipo