It sounds like you’re using a pro box in aerial mode rather than the “Freeview over broadband”/internet mode.
Freeview channels broadcast on different frequencies/multiplexes, which accounts for the difference.
For the multiplex which carries the HD channels it sounds like the signal is substantially stronger from the North Wales transmitter.
Do the correct region of HD channels appear in the 800s range of channels? Your channels from the North West/Winter Hill transmitter may appear here.
In some areas you might get a secondary region in internet mode. Extra regions will appear in the 800s range in this instance too.
