Well, here's my thinking on this; as long as the compass is facing forward (i.e. same direction scope is pointing), the readings should be just as accurate. 87* is 87* either under, above or along side the scope.

The only time I can see there being a problem, regardless of where the compass is placed, is when the object is at zenith.

When I get one, I'll mount it temporarily and see what happens if it's mounted along side the scope.

-Fred