I am new to baking bread. I made a loaf of 100% Whole Wheat Sandwich Bread and Whole Wheat Mash Bread from Peter Reinhart's "Whole Grain Breads". I made both of them in the Batard shape. During the proofing process, both loafs flattened out. The volume did increase as speciefied. It started out about 2.5" to 3" tall and ended up around 1.75". It did not have any oven bounce. I used a sheet pan and steam. I do not have a hearth stome yet. What should I do different?