Weight is, frankly, immaterial. Thickness and marbling are key. Don't cook by time, it's only a guideline and is dependent on temp; cook till done. Larry suggests the tear test which works, I use a skewer inserted in between the bones. When it goes in like butter: done.
Foiling adds a braising component. It's not a must but many foil because it softens the meat and fat effectively. Returning unfoiled re-firms the meat.