I can find references here and there to mutiplication stacking, ala the x2+x2+x2 = x4 not x6 or x8. (i.e. you stack the extra, and do not cross multiply.)
Applies in other factors, like x2 concussion hits from two different sources should be x3 not x4 by the same logic.
Many instances where the multiplication doesn't apply are listed. (Like, you cannot use two PP multipliers at the same time.)
But I can't find any reference at all to stacking of Division. . . .like if you have an effect of "One half" something laid on top of another "One half" is that "None" or "One quarter" per normal math, or "One Third" per the stacking logic for multiplication?
I can't find a rule, errata, or reference to that anywhere, so in the end, for the original question, Tim's answer seems to be the right one. . .there is no official method I could find so it's a GM call.
Unless you consider division to be the mirror image of multiplication, in which case the answer to the top question would seem to be "One Third the normal PP". (Which seems whacky.)
You definitely pulled a weird one out, Dutch.