the tarp being saturated shouldn't have anything to do with misting, a fabric that mists will do so immediately under a showerhead and this is because the fabric/coating doesn't have a high enough degree of water resistance (measured in mm). wether your tarp is saturated or not should have no effect on this, and your tarp should be pretty saturated on the outside after only a few minutes of rain as that's what happens to sil tarps, our silnylon won't mist through but it still wets out on the outside after a few mins of steady rain and that is normal for sil fabric.