Victor,
You are correct about the radius being too small for a perfect fit, however I just used blue loc-tite under it and haven't had any problem. An epoxy bed or machining the correct radius would have been a better fix, but I really don't think it will be a problem for most rifles. The biggest problem I see is that the sight will be at the top of the ramp for most applications. I put mine to the ultimate test last fall, climbing around in the Rockies for elk, worked just fine when I needed it to.
I would always prefer a slightly too small of radius on any base (scope or sight) before I wauld prefer a slightly too large radius, allowing the base to rock since the screws would be the only thing supporting it.