One thing that causes the windward rail to sink is too much weight (any weight) on the heels. Sometimes when getting used to the harness, the tendency is to lean back against the harness, but at the same time rocking onto the heels. The more weight on the heels, the more the rail sinks, and you will head upwind. Think about leaning back but putting the pressure through the front half of your foot (in the strap, both straps). You don't have to lift your heels, just don't put any pressure on them. With the weight off the heels and the pressure through the toes against the board, you will be driving the board forward, and can use the toe pressure to do a little foot pressure steering as you describe in post #13. You use the toe pressure with the back foot when you take it out of the back strap and place it on the centerline. That's good. Now do the same with your feet while in the strap. No heel pressure.
good luck and keep up the good work,