The effect of angular momentum conservation constraints on the limit of the rotational energy transfer (RET) in a diatomic molecule due to collisions with an atom has been investigated. The importance of the classical limit of the rotational energy transfer, (Delta E)(max), predicted by the hard ellipsoid potential model has been found such that it is comparable to a well known parameter \Delta E\*, given by the two-parameter power-gap (PG) "law" and the RET cross sections computed on the real potentials. Numerical equivalence of (Delta E)(max) and \Delta E\* for various types of potential surfaces over a wide range of potential parameters, collision energy and the mass of the system has been verified. The feasibility of obtaining the difference of the semimajor and semiminor axes of the hard ellipsoid potential from the scattering data and the PG "law" has also been discussed.