I think in case of the bike frame the distortion is minor. As I understand it's only there as proof of ownership for the people who really need to know on a hop

I think in case of the bike frame the distortion is minor. As I understand it's only there as proof of ownership for the people who really need to know on a hopefully unlikely occasion. So making it not too obvious might be a good idea when it comes to bike theft. The QR-Code is meant to be easy to decode, adding compensation for non-planar surfaces might make it non-trivial to implement on embedded devices.