The left-hand wiper, as viewed from the LHD driver's seat, is supposed to rest on top, according to the Haynes manual. Just looking at the structure of the wiper arms, the longer one with the greater angle must be on top, otherwise, it would not be parallel with the bottom of the windscreen when at rest.
So, is there any way to adjust the arms independently? Or, how else can I solve the problem of the left arm striking the right arm on the return swipe?