I - think - you might be mixing something up there a little! The line you posted there seems to originate from the flurry table, which takes the greater flurry feat into account, which, indeed, is not in NWN or POTM, but the base attack progression is the same still. So prolly the suggestion would be to implement that feat. (Which I dunno how feasible or wantedthat is, but well, thats for the devs to answer I s'psoe!)