Hi Richie,
I,m up in Motherwell in Scotland. I have a DPD antenna which is in the attic. It gives good coverage but would be better outside but the improvement would be at the expense and trouble of installing it outside and the neighbours may not like the site of it but I am happy with it as it is, especially when combined with the live network.
The coverage the supplied antenna and a larger antenna gives is dependant on a number of factors such as your location and the surroundings, as it works by line of sight and lots of things like buildings, hills etc can cause limitations.
Saying that you get good distance with the supplied antenna, over 100 miles is very possible. I was in Dublin recently and with it sitting on the hotel window was picking up aircraft over Birmingham. Also at Glasgow Airport and was picking up aircraft over Dublin. There are lots of factors to contend with but there are usually ways round them.
With the DPD antenna I get coverage all the way from Inverness to below Teeside over to Blackpool and over below Belfast and Donegal
Alan