First, I like say that I try to make negatives (in-camera) that require no contrast agent. So I think that this would be your #1 goal -- to get negatives that require as little contrast agents as possible. Forget your old negatives -- make new ones just for this process. After all, you probably took the old ones with silver printing in mind, and since palladium and platinum printing is truly a different beast, you should be "seeing" differently than with other processes.
The more potassium chlorate (not chloride, btw) in the final mix, the more contrast a print will have with the same negative. This is with both platinum and/or palladium salts. The more potassium chlorate one uses (the ferric oxalate Sol #2), the grainer the print will be -- sounds like you got that scoped out okay.
If one is using just palladium salts, then NA2 will boost the contrast of a print...it will have no affect of mixes that contain platinum salts. I wasted a lot of NA2 before I found this out!
Now how they work, that is a good question...I do know, sort of, but not well enough to really tell anyone with any accuracy -- so I will let others chime in on that.
The NA2 has twice the amount of platinum ions available, or something like that...so I think it acts more like a booster than a restrainer...I think your blacks will get blacker faster, relative to the highlights, thus increasing the contrast. Potassium chlorate holds back the highlights, relative to the blacks, thus is a restrainer and increases contrast. There, I just did what I said I was not going to do -- now we wait for someone to tell me I am full of it and something else really happens !LOL!