Cool. Good tips, thanks. I had a feeling that the inaccuracy was geometric, as you describe, but fortunately, all I have to demonstrate is whether the meter is inaccurate or not. If it's inaccurate to any significant degree, I'll have it switched out and sent in for testing. Hopefully, they test it under a heavy load so we get a real sense of how off it is.
A bit of blue sky thinking at this point, but good to know this is more common than I thought.
Added to the list of requirements for next house -- smart meter (second only to insulation).