If, however, the boat becomes heavy on the helm (more weather helm) and won't track well off the wind, it could be that either sail areas or sail trim, or both, are at least part of the issue.

Weather helm is the term for the boat's tendency to head up. To counteract this, you want less sail power driving the stern to leeward, and more sail power pushing the bow to leeward. You can achieve this to a certain degree by flattening, twisting and under sheeting the main, while sheeting the headsail further forward (= lees twist) and harder. You can also reduce mainsail area by reefing.

In fact, you can often steer a boat simply by moderating the amount that the main or headsail is "pulling".

The problem could be caused by too much vang off the wind (= too much power in the main), while not sheeting the headsail far enough forward and to leeward as the wind moves aft (= too little power in the headsail). Excessive heeling can also contribute to weather helm. De-powering the main should help keep the boat on its feet.

I would advise playing with sail areas and trim, off the wind in an effort to find the correct combination.