The coin-slot screws usually end up on the side with the ejection port, for no other reason than that's the easiest way to set them up in my small scope-mounting workshop, down in the basement.
The only problem I've heard of with mounting them that way occurred years ago, when a friend of mine owned a Browning BAR in .270 Winchester. Once in a while a empty case ended up jamming the action, and it turned out the reason was the coin-slot screws were on the ejection-port side: An empty on its way out would occasionally hit the screw. Turning the rings around solved the problem. But that was back in the day when the coin-slot heads were somewhat wider in diameter than they are now.
