Taking James' advice, I drove right up to the masts and there was no signal. I then drove around the new housing estates that incorporate the masts and also the new roads that immediately borders the west side the A419. No signal. I picked up a weak signal again once I had gone over the A419 bridge in the direction of Highworth.
My conclusions are: 1 The source is not in Blunsdon 2 When Dom had a strong signal when driving up the hill to Blunsdon I believe it to be a signal from further North mirrored back by the hill itself. This would support the two heading given by Marc and Viv.
