One of the reasons I prefer a full vest is that the vest acts as another layer of protection from the sun. Think about the way desert tribes dress in layers to ward off the sun. The vest provides some of the same protection, but without the chimney effect. A few years ago I started wearing a long sleeve compression shirt in a light color as my first layer (UnderArmor or equivalent), then a light, loose t-shirt, then the vest over those. Seems to work.