After a monster year for the stock, this move looks less like doubt and more like a textbook decision about concentration risk, timing, and discipline.Massachusetts-based East Coast Asset Management cut its stake in Perimeter Solutions (PRM +0.32%) by 497,847 shares, reducing its position by an estimated $6.40 million, according to a November 14 SEC filing.What HappenedAccording to an SEC filing dated November 14, East Coast Asset Management reduced its holdings in Perimeter Solutions (PRM +0.32%) by 497,84 ...