Sheep just scratch when they're fairly relaxed - unlikely when a stranger is near - unless they're ill.
The rounded hill on the horizon has a profile similar to those found in 'harvest hills'. It doesn't seem uncommon for one of the edges of an upright single stone to be broadly aligned on such a hill - and sometimes the sun will set behind there on a certain day or pair of days ...
'Hag' is an old word for hedge, incidentally ! Still found in the 'Hague'.
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