According to the rules when you use a weapon kata you must add the difference between the maximum hits you can deliver on that specific AT with the weapon and the MA to the conussion hits you deliver.
So for example if you use Sweeps and Throws Rank 1 with a Whip on AT 15, you have a bonus of 8 (whip) - 4 (MA Rank1) = 4 concussion hits.
Uh, what? I think you're doing it wrongly. As written in AL&CL, "…and the maximum number of hits that can be given to the AT being attacked by the martial arts attack table being used." There's absolutely
NO mention of a notion of rank, but indeed "the maximum number of hits (of the) martial arts attack table"!
In your example, the additional damage is 8 (max. damage of a whip vs. AT15) - 8 (max. damage of MA throws vs. AT15) = 0!
Also, I believe that the additional damage are only to be added when the original damage is at least 1. At last, you may want to decide that this additional damage is
not affected by damage multiplier (i.e. it's added
after damage multiplier is taken into account).