TDK,
16x16 should be big enough for sighting in though 24x24 can help catch the shots a bit better. You may be hitting right at the edge and not able to catch it. With your new scope, try starting off at 25 yards and I suspect that will catch problems a bit more readily and eliminate some frustration in the long run. While I never sat down and worked out the geometry, even with boresighting, you could be off several inches at 25 yards and it will only get worse at longer distances. Also check the leveling of the scope.
From your response I can see why you noted the bending problem from the rings, which still goes back to problems in mounting procedure rather than the rings. Why not consider mounting the scope yourself in the future as it sounds like the dealer may be bending scopes on a frequent basis. Tain't hard to DYI and can easily be done with a few simple tools as long as you go slow, stop to check your work frequently, and avoid overtightening.
Good luck and safe shooting.