IMO, the eye box of the 3.5-15X50 NXS is very similar to the 3.5-10X40 Leupold. both are user friendly.
in fairness, the eye box on the 5.5-22 is probably a product of the physical/optical properties of the scope, (magnification, size, ect...). the 56 mm version would undoubtedly offer more exit pupil making alignment with your eye less critical, but i don't know if it would do anything for the 'depth' of the eye box. the 5.5-22s i had were both the 50mm version. i refuse to suffer a 56mm scope on anything.
as always, selecting optics is all about balancing the compromises to suit your needs.
