allowable area increases

[my911]

existing bldg - 11,500 sf
clear space all sides greater than 20-ft

adding 11,000

final SF = 22,500

type II B construction non-sprinkled
allowable Area tbl 503 = 14,500

F = 664 (after additions bldg W greater than 20-ft)
P= 664
W= 20
If = (.75)x.67 = .5
Aa = 14,500 X 1.5 = 21,750 sf

chap 706 - party walls - I can separate additions with a section of 3-hr rated wall Tbl 706.4- but tbl 508.4 - for occupancy E - no sep required.
what am I missing. we do not meet all of 507.10 criteria for unlimited area.

thanks for connecting dots.

[Jake1402]

I know this is way late but what code and year?