The answer is that back in the old days where armies still carried flags into battle, they would always want to portray that they are advancing. If you imagined the reversed flag patch as a large ceremonial flag, it would appear (from the right) as if the soldier is moving going forward, and not retreating. If the flag was on the left, it would be regular. I know NASA does the same with the space shuttle, but I'm not sure about other agencies that operate flying objects
