Ian,
First check the bead molding line just above the rim sidewall; it should be an even distance from the rim all the way 'round if the tire bead is seated properly. Once you verify the bead is seated evenly and fully, then you can objectively assess how much and where the tire is ovalized, and perhaps even document it for a warranty claim.
Often, I've found the reflective strips on tires are slightly misapplied, leading to an out-of-round appearance, as you already know.
More rarely, I've found there can be anomalies in the way the tire itself is molded and constructed, resulting in a "hop" as that part comes 'round. If it is severe, it can be noticeable when riding. The support section of Shwalbe's website has a section telling what to do to photographically document tire defects for a warranty claim. Unfortunately, I've found some of my Schwalbes are ovalized to a disturbing degree, but it is almost impossible to capture in a single photograph. Video would do the job, but there seems to be no way to submit vdeo for a warranty claim. I need to pursue this issue on my own, but lack the time at present to do so.
Be sure to check the tube is not bunched-up inside the tire. Also, is the "bump" over the valve stem? The bead can still be seated but the profile rendered a little "off" if the valve isn't fully seated.
Best,
Dan.
