I believe it is a little more complicated than that as groups are assigned by seat so back of the plane windows would be in the B group.
Right from their page "We now board by groups with a method that utilizes the entire length of the aircraft and is determined by your seat assignment—"
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I believe it goes like this:
Pre-Boarding for customers with disabilities
Mosaic and Mint® customers
Even More® Space customers (Group A)
Courtesy Boarding for active military personnel and customers traveling with children in car seats or strollers.
General Boarding by group:
Group B: window seats in the back
Group C: middle seats in the back + window seats in the front; then
Group D: aisle seats in the back + middle seats in the front; then
Group D/E: aisle seats in the front No E on E190's.

More than one person on the PNR all tickets get the earliest qualifying boarding group