We study above-threshold ionization (ATI) of atoms in strong elliptical laser fields. Recent benchmark experiments for H showed that the attoclock offset angle related to each ATI ring increases remarkably with energy and this characteristic phenomenon can be attributed to the laser-induced nonadiabatic initial velocity and position of the electron at the tunnel exit [Phys. Rev. Lett. , 273201 (2021)]. However, the specific mechanism remains unclear. Here, we calculate the photoelectron momentum distribution (PMD) through numerical solution of the time-dependent Schr{"o}dinger equation (TDSE) for atoms with long-range potential (LP) and short-range potential (SP) and the use of the strong-field approximation (SFA) and a Coulomb-included SFA-based model. Both the TDSE-SP and SFA results show a sudden jump of the ring-resolved offset angle from $0^{\circ }$ to ${90}^{\circ }$ as the ring energy increases. Our model-based analyses show that the yield maximum of a low-energy ring relates to ionization near the peak of the major-axis field, whereas that of a high-energy ring relates to ionization near the peak of the minor-axis field, resulting in this jump. The Coulomb effect smooths the sudden jump into the gradual increase observed in the results of experiments and TDSE-LP.