Lobster-eye optics has been proposed as a high-energy detection device with great potential for astronomical observation and safety inspection due to its large-field-of-view (FOV) focusing ability. In this paper, we study the relationship between the optimal structural parameters of the meridional lobster-eye lens and focusing efficiency. The maximum odd-reflection component, which relates only to the FOV and the channel ratio of depth to width, has been found. Furthermore, the structural constant C, which determines the optimal efficiency structure of the meridional lobster-eye lens, is revealed for hard x-rays. Meanwhile, by introducing accurate reflectivity of iridium in soft x-rays, the constraint of the effective FOV with respect to x-ray wavelength is analyzed. The research results can help to design the optimal structure of the lobster-eye lens in multiple spectra.