It was always said that tannin extraction starts at 170F. So I stay a bit below it. Not to mention,the higher the mash temp,the less fermentable so the book writing experts say. The lower temps give plenty of color & fermentability. And you def do not have to mash on the heat to maintain a good mash temp. I get the BK/MT wrapped up in my thinsulate lined hunting coat for the 1 hour mash after being well stirred. It gains 1 degree over the course of that hour rather than loosing temp any other way.
And now they say it isn't temp,but PH from water volume that extracts tannins. Whatever. I'll take a chance on neither. Better safe than foolish saying whatever,I'll do what I want cause it worked before. Maybe that's true. Someday it may not.
Sometimes I just don't understand these pro guys saying X for decades. Then turn around & say Y is doing it,not just X. What the F ever.