It seems that whenever I see a shrimp cocktail served in a restaurant, the shrimp are always plump and gently curved, yet, whenever I cook up a batch of shrimp they always get tightly curled. I defrost them first, then put them into boiling water, let the water return to a boil and cook them a minute or two longer. Then, when they're finished cooking, I drain them into a collander and run cold water over them. Is there something I can do differently to have them retain more of their original shape? Thanks!