I shoot for probe tender in the thickest part of the Flat. If the thickest part is probe tender the rest of the brisket will be amazing. Don't over think the process. Forget all that BBQ pitmaster comp Bull Feces nonsense. it has ruined more good meat by inexperienced cooks than I have raised in 10 years. It is really a simple process Constant temp, meat & time. I learned from My Grand dad and My Dad there was no thermometers, foil, injections and 30 ingredient rubs. Post oak & Mesquite, salt & pepper, Time & meat. Really that is all you need and some coldbeers to pass the time. There was a time when I went rouge and tried all that silly Snake oil and dropping my temps to the ridiculous 225. I was chasing rainbows and exposed me to all sorts of unnecessary problems. Once I came back to the basics I saw how stupid I really had been. K.I.S.S.
I'm a Proxy Vegetarian> Cows eat grass & I eat cows.