Printed from: https://conservationhandbooks.com/dry-stone-walling/technical-walling/coping-on-slopes/
Amongst wallers there is considerable debate as to whether the topstones should be placed on the true vertical, sloping uphill or sloping downhill. Most written sources suggest that sloping uphill is best, arguing that topstones tilted uphill bind most strongly, because as the wall settles they are pulled more tightly together and held by friction....