Because, frankly, taldren doesn't even bother to consistenly follow their own rules. Not only that, the shiplist they have is full of errors.
Quick check of ISC carriers, first number fighters it carries in SFB, second number number of fighters in SFC:
CV, CVZ: 12, 12
CVA,CVAZ : 24, 16
CVE, CVEZ: 8, 4
CVL, CVLP, CVLS, CVLZ: 9, 8
CVS, CVSZ: 12, 8
As can be seen here, the fighter numbers using taldren's own rule of thumb for the CV (and variants) and the CVL (and variants) is too high.
As for ISC fighters having problems, it's not Firesoul's fault that taldren inexplicably decided that ISC fighters should not carry the plasma torpedoes that they carry in SFB. Send complaints on this to the game designers, as he has no control over that.