Maybe I'm just not used to how much play exists in fatter tires?
The same % variance will look larger on a larger tire, yes, but it sounds like the tire itself is probably okay. You are looking at the correct witness marks, right? I don't presume to insult anyone's intelligence, but it may be worth nothing that things like reflective stripes are often not uniform around the tire and the witness line/molding at the bead itself is the right mark to check. You're probably looking at it correctly, but I thought I'd mention it nonetheless.
Do you see a "hop" or a "dip" in the tire as you spin it? If one small area of the bead stays a little sunken still, that area should have a slight dip in the tread. You may also notice a small lateral (side to side) shimmy when spun. If neither of those are objectionable to you and you can't feel it when riding, then it's probably okay. In the realm of larger tires, I've had some that spin about as true as true can be, and I've had some that always have some nonconformity to them even when the bead is seated correctly. These don't tend to be made to the precision of automotive tires, unfortunately.