Approximately 20yards-long steps-from the patterning board. Chokes give us inches in width, but we most often miss in feet.
Dead nuts center a Bird and you get ground meat with all. However, the tight two, will give you a cushion when the distance moves out. Less junk on the fringe also means you will cripple less closer.
As Bob mentioned above, a pattern can be deceiving in that a Bird normally will not be hit with all of the hot center, in that it is passing thru a longer string than represented in the 2 dimensional plate pattern.
Addition: This is a top tier shot shell, a Fiocchi 1oz, Little Rhino, 7.5's that I suspect will pattern tighter than most factory upland loadings
IC: Call it almost a 14 inch spread.
LM: 12.5 inches.
Mod: 11.5inches.