Thanks for direction Nick. This is definitely useful information in helping me extend what I know of the coverage of GRAVES radar. The scatter is from lobes from the rear of the antennas. The end of the trail crosses the Great Circle line between my monitor receiver and the transmitter close to Dijon and is just about midway between. The power profile I recorded suggests it is specular scatter which, because of where, implies it is at a fairly shallow entry angle.
Thanks again Nick and Eric – keep them coming!