Conspiracy theory - they could have moved the check in desk into that space and expanded each lounge a bit. The 20 seats in the diagram doesn't make a ton of difference. The design motifs are extremely similar between the 2 lounges. My guess is that if the FL becomes consistently overwhelmed, they have the option to close the AC indefinitely and convert the space into a larger, single, FL space. The 'flex space' is essentially the walkway needed to let passengers walk between the two halves without going into the reception area.

Also, a ton more pics at TPG: https://thepointsguy.com/news/americ...-philadelphia/