I just had my first sip of coffee, Len, so I'll see how math goes.....
My starter is actually 100% hydration (50/50 water and flour.) The 20% I referenced was how much starter I put in (20% of the weight of the flour in the main mix.) SO.....
1200g Flour in main mix
120g Flour in starter
840g Water in main mix
120g Water in starter
1320g total flour
960g total water
water divided by flour leads me to 72.7% hydration overall.
Ok, that hurt my head, need more coffee....