Your internal LAN subnet has nothing to do with a "1:1 contention ratio".
In the UK, an RADSL (Rate Adaptive Digital Subscriber Line) connection usually has a contention ratio between 20:1 and 50:1 per BT guidelines, meaning that 20 to 50 subscribers, each assigned or sold a bandwidth of "up to" 8 Mbit/s for instance, may be sharing 8 Mbit/s of uplink bandwidth.
