Covering the entire south wall as well as the first few feet of the kennel is ideal. Of course, you need to customize this to your particular yard and its periods of sun. I try to shade so that this time is early morning or evening, when the sun is the least intense. You should probably shade from late March to October, if possible. The surface that your dog lays on during the day can also playa part in his comfort.
Asphalt is out for many reasons besides heat conduction.
Concrete can also become warm. While it is not as uncomfortable to the touch as asphalt, for example, it reflects a lot of heat and will make your dog hotter. Your dog should have a dog house or wooden pallet to lay on to keep him off the concrete surface. The dogs are most comfortable with grass or dirt to lay on. And I say dirt, because that's what the yard will look like after they lay on it for awhile.