hi Andy .It was the O.S. who said the "hollows are not true cups" , they also unsure of whether the Tullpowrie stone (the other one if you get my drift) was man made either , that is certainly not natural ,as for the Clach I think it may have have had some natural hollows but they have been worked ,and there are some genuine cups too.

I would say that it shouldn't be standing up. It should probably be lying down, because I'd say it is a bullaun stone

http://www.megalithomania.com/show/image/3862

I reckon they look man-made

nice one