Thanks for that Bratters, will trial & error basically. I am just concerned that rather than positioning I losing distance because of the length of cable now involved between the Radarbox & PC.
No, not if I understood you correctly. The length of your USB cable is immaterial in terms of degrading signals; it's aerial cable that is responsible for signal loss.
I'm currently using around 12 metres of USB, but the aerial cable is the supplied one. Signals were never better.
Do let us all know how you get on and whether you can come up any "scientific" theory for siting your aerial in the optimum position - if and when you find it.
(I find a stack of cardboard boxes and biscuit tins come in handy)