If you look close at most of the tires that come from S.T. it looks like the guy who put the paddle on the casing is drunk, blind, or both.
That said, always install them refrenced the same. (align the valve stems) Make a few passes with the tires the same pressure (my number was always 4psi) then check pressure to be sure they are both at 4psi still and then measure RO. Most sets will be a different RO at a given pressure. Add or subtract as needed to make RO equal. Once you've established that you can add or subtract for track conditions if you wish.