Aha, I have misunderstood Roxy Bird. I thought you meant that you had turned the Garmin from the usual wristwatch position to a position where it is on the edge/top of your wrist and so points its face directly at the sky for more of the time.

This is what I did and it appears to be much better now. I thought that maybe now it sees more sky instead of pointing half its field of view at the ground.

My 101 started off very well and beeped at the same place within a foot or two on the way out and at my garden gate on the way back. Suddenly, it has taken to beeping still at exactly the same place on the way out, but on the return home beeps about150-200 metres too soon. The landscape is fields with a road with some overhanging trees. But why does it only affect the return run?