I'm not new to percentages, but I'm new to sourdoughs. I don't know why my brain won't wrap around this so if you guys can double check my math I would appreciate it. 

I want to make a sourdough at 70 percent hydration with 20 percent of the total dough coming from the starter. The starter is 100 percent hydration . 2% salt....

I have the following percentages...

Flour        551
Water       385
Starter      240
Salt             24 

The final dough should be around 1200 grams for two 600g boules. I got these numbers by setting the sourdough to 20 percent of the final dough weight. Salt came from the same. I took the remainder of the dough weight, i think was 936 or something, and set my flour and water to that keeping in mind the starter was 100 percent hydration.

Am I way off?