Oooer, okay, don't shoot me if what I tell you is totally wrong, but I grow my toms as cordons, so only one main stem, I pinch out all side shoots so all the plants energy can go into producing fruit, and not lots of branches and leaves. I believe our learned John Miller told us a while back that the lower leaves stop working efficiently, so they can be removed allowing more energy upwards. Also, if there are masses of leaves, there can be poor air circulation, so the risk of disease in the still air, plus, yes, less light, and less heat due to shading, so what I have done, please don't shout everyone if it is wrong, is remove all the lower leaves up to the first truss of fruit, then after that, just trim some off if they are really causing dense shade. I guess, if I had more room in the greenhouse I wouldn't have to do this, but as I have lots and lots of plants all crammed in a small space, they are all shading each other, so it was more necessity. I should imagine I have reduced the leaves by 50% per plant - hopefully leaving enough for photosynthesis to take place successfully! Finally, my toms have all started ripening, and some of the trusses, especially the plums, are huge with 12 or more toms on one truss!!!
