4 pounds and triangular sounds more like the point. Which is commonly used for burnt ends, and will have a higher marbling than the flat. The flat is typically more rectangular in shape and leaner. When connected to the point you have a packer. The weight of a packer would be in the 15+ pound range.
This is one of the est brisket posts ever posted here:
That makes a lot of sense. Yes, it is highly marbled.
Does that mean I'm going to be doing something entirely different from what's been posted here as this thread... ok I see n the thread you've posted around page 5 they start talking about separating the flat from the point.
I think you'll smoke the point the same as the flat. It's funny cause I just saw a rerun of pitmasters in Kansas city and they had to cook a point brisket. It seems typical that you'll be making burnt ends out of that and would have a tough time getting nice slices due to the higher fat content.