2. clipping is a GPU fixed function done on x,y,z axes separately, so it will always be a planar cut

3. the effect you're talking about can be entirely removed by setting the frustum's near plane to fit within your collision hull, e.g. for a spherical collider

    function near_plane_meters(collider_radius_meters, width_px, height_px, focal_length_px)
        return collider_radius_meters * focal_length_px / sqrt(0.25*width_px*width_px + 0.25*height_px*height_px + focal_length_px*focal_length_px)
    end