PJ,
You can improve your chances of getting a site that fits by arriving as early in the morning on your arrival day as you can. That way the Front Desk folks have more sites to work with. If all the longer sites get given out that day to other arriving guests by the time you arrive, there is less for the Cast Member to work with. They swap pre-assigned sites quite a bit before you get your Early Check-In text (if you used Early Check-in on-line) or arrive in person and check in in person. Once you arrive in person (even if the site isn't ready yet) or the early arrival text goes out, that site is locked in as yours and not swappable.
So get there early if you can work your travel schedule to do so while they can still shuffle the deck. That's all you can do at that point. Good luck!
Bama Ed
PS - you probably already know this but I wrote it out for the benefit of those who don't