I don't know but all mine lean, even the one in near full sun; yes, mine in the front most lean a little westward, too. The only thing to do is make sure they are getting the right nutrients plus I got about 36 hoop stakes at Home Depot that work well for the shorter ones (as opposed to the 5-6 foot ones). The hoop stakes are green, heavy gauge wire, the hoop has an opening you can push the stem into and hold well, not very visible, fairly cheap.

Some I don't bother with, just let them lean, some more, some less. Oh, the color parade ones in the back do not lean but they're odd, shorter with enormous blooms. I'm sure they are not the newer pixie lilies, just odd for that variety.

Also, I was spraying the foliage on cooler, cloudy days with kelp solution when I got around to it. Also, when I first put them in, I was spraying with Liquid Fence, stinks but don't mind. Expensive but goes a long way. Haven't had a problem with critters bothering any of my lilies yet though. Some have an awful time with deer.

I'm disillusioned with the orientals. They put on a good show but bloom such a relatively short time, think I'd rather have something to replace them with a longer bloom time.

I do feed them with Scott's Bloom Booster, don't scratch it in, once in the spring and once in the fall if I'm on top of things.