I went through the same thing with my first Tarptent. Henry Shires suggested more stripes! I suspect that your three small stripes are probably not enough. Try more--but do as circular spots rather than stripes (easier to clean trash off the floor). Also put a few spots or strips on the bottom of your sleeping pad (under the pressure points, hip and shoulder). Silicone sealer worked on my old POE Insulmat and my even older Thermarest, but it doesn't stick at all to my current pad from the late lamented KookaBay. I used urethane based seam sealer on the last after all the silicone peeled off after a couple of trips. I have no experience with Exped--you'll need to experiment.
Do note, however, that if you're on a slope, gravity will win every time. I've gotten used to it, although one time I woke up almost out the door (side-opening tent) with my dog (on the uphill side) sleeping on half my pad! I'm still not sure whether the migration was altogether due to gravity; part of it may have been my dog's seeking a more comfy bed and pushing me off the mat!