I have never been anywhere in the UK yet where I could not receive 648 to some degree. That includes areas like Yorkshire, Hampshire and Dorset , Sussex - East and West and the home counties. I live in the TSA in Essex so get a pretty strong signal all the time in my home area. I'm not sure that more power would return significant returns but as the main rig is capable of much more and there's some free electricity coming it's way it could be worth running around 10 to 15KW to see what difference it makes. It's already comparable to what it ever was from the North sea in terms of coverage as it is.