You're mixing lots of things up here. "It will dry out" has everything to do with the amount of heating and nothing to do with its evenness. Soups/sauces heat well despite uneven heating because of secondary effects like better convection/conduction (not sure which particular effects are more significant) due to the sheer amount of water relative to the rest of the food. The water distribution of the food is not the problem here; the problem is the radiation pattern. A uniform radiation pattern and uniform water content will give you even heating, and a water content that exactly compensates for an awful radiation pattern will also give you even heating.
