I am in SW Spain, and the sun and heat here are brutal. When I started growing, my main concern was to give the plants as much sun as possible. Now, my main concern is actually to protect my plants from the sun. (I am growing "on the roof" where there is basically direct sun, all day long, and temps and sun is crazy basically all year long). Sun Shade IS A MUST here. I placed an approx. 6x4' shade that way so it protects my grow spot in the biggest heat of the day.
For hardening, from the greenhouse to up on the roof, I put them for a week in a more shadier spot, and then move them to the area under the shade. Not sure what percentage that shade is, possibly 30-50%