YES, perfectly normal... the site base is spring loaded (twist it straight and see, it will return to the slightly "canted" position. It does not cause accuracy issues at all. I shoot High Power matches at 600 yards and it's not an issue.
SOME people believe that at that distance, reproducibility is an issue as you can put 10-20 minutes on going from 100 to 600 yards. WOP, Compass Lake, Accuracy Speaks and some other competitive smiths offer site bases with 2 or 3 "pins" that hold it straight, if you're so inclined. Obviously, you'd have to ship your upper to them, so that it can be drilled for the pins.
There is a company in WI, I forget who at the moment, that sells A2 site bases with a little "bump" welded on the forward side of the base to hold it straight, but I think that's just a single point that rubs up and down. At least with the whole thing sliding as you add elevation, it won't also torque vertically around that little "bump"