OK, I went down today to try for it today so I'm going to answer my own question in case anyone else might be interested. The location "250 yards" west of the crossroads" is fairly easy to find and consists of a stretch of about 30 or 40 yards of reeds by the side of the path. Viewing is very tricky here as the reeds are rather tall. We had no luck when we were down there from about 7:30 until 11 a.m. but I later spoke to someone who saw it the previous day and he said that the main area to watch is at the east end (the end that you come to first from the crossroads). There is an indent here right next to some Sallows and the reeds are thinner. He did say that it he saw it for all of 3 seconds out of 6 hours of waiting which gives a good idea of how hard it is to see.
Just to add further confusion, today on RBA it was instead reported 100 yards east of the crossroads in reeds - whether this is just someone mis-reporting the location or the bird has actually moved I don't know.
Plenty of Yellow-browed Warblers about and I heard one which sounded a bit more like a Pallas' but who knows. Got nice views of the Great Grey Shrike in the Burham Overy dunes and a brief view of the Olive-backed Pipit at Wells by way of compensation for the lack of Radde's.
Hope this is of some use to someone.
Adam
