The maximum conversion ratio is relative to the highest degree of undermoderation, which is fixed by the necessities of heat removal. But before this utmost limit is reached, other conditions lowering the conversion become effective. Besides safety-relevant coefficients of reactivity and high fissile inventories, there are other symptoms of a potential economic disequilibrium, which can be visualized by examining the whole domain between the highest possible undermoderation and that of today. The physics underlying the changes in fuel recovery have been investigated by studying the neutron balances and the results have been summarized.