Steering close-hauled in darkness is largely a matter of feel. As the boat falls off the wind, heel angle may increase. She'll start to slow down when she falls off 15 degrees or more below her best course. But when she luffs above the optimum course, she will come upright and lose some of her way before the sails begin to complain audibly. It's easy to feel the boat coming upright, so being high of the course is more easily recognized than being below it. True expertise on the helm comes with time. If you're still waiting for it to happen to you, try creeping slowly up to windward every few minutes, wait for the symptoms, and then head off just enough to get going again. Note the compass heading, stick with it for a while, and then repeat the experiment. You won't go far wrong.