There are 11 active judges in the D.C. Circuit.
Okay, that explains where 11 comes from for en-banc...
But, today's 3-member opinion then has 2 that are not one of those "active" 11 - they are listed as currently being a "Senior Judge". That would mean that the en-banc 11 would NOT include two of today's judges (one voted for, one against; the third is one of the "active" 11).
United States Court of Appeals for the District of Columbia Circuit