I'm not all that well versed in preferments, but I did check the main calculator, and, from what I can see, it looks good.
Does 1 teaspoon of yeast really weigh 1.86g, and, conversely, is 1g of yeast .54 t? Is this true for both IDY and ADY?
Edit: Something's not right with the yeast. The dough calculator has .33 t. of IDY per gram and .26 ADY per gram