I planted a small specimen of Rozanne as my first geranium this spring. It has spread out to at least 18" so far and is blooming.
We had about 6 weeks of cloudy rainy weather after I planted it, but the past 2 weeks have been increasingly sunny. At this point I think growing conditions are especially good, with mostly clear skies but no serious heat. The plant is located where it gets about 4 hours of direct sun, mostly morning and very early afternoon, including some reflection from being near a white painted wall. The ground is mulched and the soil is moist.
What concerns me is that the leaves curl up pretty badly whenever the sun is on the plant. It really looks like it's withering away, then recovers once it gets some shade. I had to prune back one branch that was permanently damaged, but otherwise the plant looks good when it's shaded.
I'm wondering why my Rozanne seems to be having so much trouble tolerating the sun. It's mostly in the morning and the temperature today was only 75 degrees. All the plants in the same general area are newly planted this spring as well and they seem to be doing fine - even a couple that I thought might need more shade.
I have this same plant (2 of them) and One gets a full days morning and early afternoon sun and the other full sun all day. Both do just fine and are thriving. I am in zone 5a Chicago. Perhaps your soil needs amending or more deep watering. Or quite possibly you recvd a mislabeled plant (this happens).