Nikon Red Dot Mounting

A was recently attempting to mount a Monarch redot on both a Weigand weaver style base and a Weaver made base and noticed that when I mounted the red dot and started to tighten the screws, the floating half of the mounting base next to the socket heads was not perpendicular to the base, it was actually cocked, as if the base was to wide or the Nikon mounting system not made right.

Anybody else experience this? What specific brand manufactured weaver bases did folks use that did NOT notice this? I am mounting on a S&W 686 .357. I did speak to Nikon, but they could not offer any specific advise.

Thanks-

Dave g