If your wash finishes at 10% alc, then 10% of your wash is pure 100% alc. If the alc comes out at less than 100% pure then there will be more of it.
I'll put it in numbers as litres, (gave up pints and gallons long ago), and throwing oz into the mix is sure complications. You have 20 litres wash brewed to 10% alc. 10% of 25 = 2.5 litres pure alc. It comes out at 95%, or 60% alc/water. You will have 95% or 60% pure alc in what comes out. Then you make the cuts and should only be drinkin the hearts which can be as much as 1/3 of the total output. So out of your theoretical output of 2.5L, you may be drinkin 2.5/3 = about 0.8L pure. That may be about 1L or more because it won't come out pure. Thus expect to be drinkin 1 litre hearts out of a 20 litre wash, about 1/20th of what you brewed. The heads and tails can be stilled again to yield more hearts.
More sugar in the wash (brew) = more alc when the brewing is finished. Bakers yeast will survive up to 14% alc and turbos can survive in a 18% alc wash before getting poisoned and dying. Best go to a max potential alc of 12% by only giving enough sugar to get to 12%. Dying yeasts give off a nasty flavour, so do turbos when they are driven past the 12% mark.
Why brew to more than 12%? Pure greed! And there is a price to pay. Brewing to higher than 12% is false economy.
Brew long enough to let the yeasts eat all the sugar. Let the yeasts settle to the bottom so they don't get into the boiler. Still long enough to get all the alc out of the brew. Then air it and make your cuts.
cornflakes...stripped and refluxed