When reaching, particularly at wide angles, because of the point at which the head-sail sheet makes contact with the leeward fairlead, the headsail develops a large horizontal curve unless the clew is held outboard with whisker pole or by a twig to the end of the main boom. Such curvature causes flow to separate early on the headsail, making it inefficient, but, also, directs the air-flow on the weather side of the sail back and into the leeward side of the main, i.e. "back winding" the main. Depending upon the wind speed and apparent wind, as little as 25% of the aft end of the main may be generating power, which is far aft of the center of lateral resistance, hence weather helm. Either figure out how to rig a twig for you headsail sheet from the end of the main boom or simply roll in some of your head sail and move you lee fairlead forward to the widest portion of the yacht.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."