Run up into wind is a relic from the days of the spitfire with a liquid cooled engine and a small radiator the thing would overheat at the drop of a hat so all the help that it could get in the way of cool air was welcome.
Pointing a modern aircooled engine into wind makes no diference at all in practice and just gives slightly more RPM on the max power check .
for C of A airtests the run up is required to be done cross wind so a true max RPM can be seen.
How ever i think that the run up should not be done with a tail wind as the max RPM would be low due to a high prop angle of attack and for taildraggers pointing into wind will reduce the danger of the aircraft weather cocking in gusting wind conditions.