Oblique plane microscopy (OPM) is a single objective light-sheet microscopy which performs three dimensional (3D) imaging by axial scan of the generated light-sheet. Recently, multiple techniques for lateral scan of the generated light-sheet in OPM have emerged. However, their suitability for geometrically distortion free 3D imaging, which essentially requires a constant tilt light-sheet scan, has not been evaluated. In this work, we use a geometrical optics approach and derive analytical relationship for the amount of tilt variance in planar mirror based scanned oblique plane illumination (SOPi) arrangement. We experimentally validate the derived relationship and use it to arrive at an optimized scanner geometry and to understand its associated limitations. We also discuss the effects of scanning on optical aberrations and 3D field of view in optimized, tilt invariant, lateral scanning OPM systems.