That depends upon where you live and what you mean by "a little less sun". If you live in Southern California, your sunlight is denser, more intense and saturated than if you live in Upstate New York, or Britain. Most rose books are European, and they repeat the same information that roses require "full sun". Perhaps, there, they do. Here, particularly in the desert, "full sun" will often stunt the plant due to the intense heat and dessication.

Here, just north of Los Angeles, Lynnie is very happy in four or five hours of sun. Of course, she blooms more heavily in more sun, but the hotter that sun is, the less time each bloom will last. At the beach, two blocks from the surf, she did splendidly in five gallon cans with half day sun, and even some of that filtered through palm fronds. Does that help?