Long term RSL's on medium wave AM are usually 1W erp, there are a few exceptions on the ofcom database showing up to 4W. One watt should put a good signal into Felixstowe and of course Harwich and Dovercourt and given the sea path up to Ipswich I would have thought should be listenable there. Its at the top end of the band which counts against it for propagation further inland. So I would expect it to be anorak quality fading to noise over 10 miles or so inland.