I am new to using sourdough. In Peter Reinhart's book on multigrain breads there appears to two different amounts of mother starter referenced and never explained. I some recipes he take a small amount (2.5 oz) and adds it to the other ingredients in the biga. Other times he just says to substitute an equal amount go starter for the biga. I think I must be missing something or maybe I makes no difference. Would appreciate any insights.