This is my first winter with a pool, so I'm still learning, but I've had pretty much the same issue as you. I lost the cover into the pool in December sometime. Dumped a bunch of leaves and stuff in, which should be loads of fun to clean up this spring.
I'm out in the middle of nowhere, and have major wind issues. I have a 18 x 33 oval, and the winter cover is 37' long if I recall correctly. I have the cable tightened as much as possible, and a few weights that are laying on the ground, but tied to the cable to keep it down. I also have a large amount of water on the cover...probably about 6 inches. Large amounts of water were the only thing to keep the cover from billowing in the wind like a parachute, but I then started having problem with the water not staying evenly distributed. It would be a foot deep on one end, and nothing on the other, because of the wind. I finally added milk jugs, 1 per section of the pool, filled them 3/4 with water, tied them to the cable, and laid them on top of the cover to weight it down and keep the water evenly distributed. Worked in all but the worst winds. Now...I actually have two tires laying on the cover on the west edge of the pool. Took me all winter to get this figured out, but the cover is staying on now. Had high winds last weekend, and having 20-30 mph winds today.
I'm going to add a deck next year, so I'll get to start all over with figuring out what it will take. Good luck!