I could probably reduce the heat issues somewhat just by using a fan - I have several but omitted that deliberately because I wanted to see what the plants could do in the circumstances.
Overall though, I might get better results by adding a layer of plastic. It's amazing how plastic diffuses the light and you don't get the same scorching effect as under glass. The plastic would help with early season heat retention as well...
Next year I'll be back to starting extra early, let them tough out the cold weather and set their hearts out before it gets too hot.
