I'm guessing they can take full morning sun, at least, in your area. That's the problem with growing them here; I can't keep them cool enough to maintain growth through the summer except in complete shade, where they won't bloom. Where you are, I'd just give them some sun protection during the hottest part of the day (and that may not even be necessary), give them good drainage, and guard against overwatering - they may wilt in the midday sun, but that doesn't necessarily mean they need water.

I recently moved to the desert and want to keep my tuberous begonias happy. They are in shade and watered a lot, have suffered some heat stress and are not blooming. I am going to bring them inside because even when I lived on the coast I had a non-stop red that I would have in my well lit kitchen during Cmas time and it bloomed a lot there. I misted it often with a weak fish fertilizer and water. Here I have a sun room addition that is heated and has a swamp cooler, hopefully it will live in there. I will let you guys know if it works or not.