I would say removing the foil over the soil is a good idea. I'll admit that when I first saw that I thought it was genius haha, but I overlooked the same thing you did... the evaporation.

Im still worried about the drainage though. is your soil more composty/soily, or more woodchippy? have you added perlite at all? I personally use miracle gro potting mix... it works really well for me. but even with a woody soil like that, i still added about 25% perlite. If you haven't added any perlite, I'd highly recommend it. I'm willing to bet the current droopiness is from the most recent watering. Every time I water my plants droop for about 12 hours or so. I don't even know if this is common, but it doesnt seem to be a problem.