Once they are established, they probably will survive the full sun. However, they probably will wilt on every hot day, and they might not flower as profusely as if they received some shade. If the wilting bothers you, you should return them. If not, then enjoy. :) I myself have about 10 ES in mostly sun. The ones that receive more shade have many more blooms, but those in the sun have some too.

I just moved one this spring to a morning sun only location, since it never did well in it's fuller sun location. It's in it's fourth or fifth year, can't remember exactly. I've already noticed how much better it's doing with more shade...and it didn't wilt at all today!!! We hit mid 90's, too. I'm about 20 miles west of Chicago.

Thanks for your comments. I will keep them where they are and see if they will be more tolerant of sun next year. If not, I may need to move these two ES to some place with more shade.