This one's for the theorycrafters and game design nerds out there.

Suppose you had to make a "D4" and a "D10" for this dice system. What would those look like?

I ask because I'm working on my own set of mechanics loosely based on FFG's narrative dice, and this particular aspect of things is outside of my depth.

i think it would just be more dice for the sake of more dice... ie not necessary.

Apparently the d12 was used rather than a d10 because the symbols fit better on the die faces

Well its a bit more complicated than just "more dice", since the way the dice pool building works in what I'm doing means you're never rolling more than 3 good dice & 3 bad dice. Due to that and some other things I don't have room to go into, a wider selection of dice is favorable.

I probably won't be directly mimicking the FFG narrative dice either, but some insight on how you might spread it out over a d4-d12 would help me puzzle it out.

I have been using standard d4s-d12s, but there's more math to crunch on than I want there to be at a glance. So, since one of this dice system's strengths is the ability to easily read your results at a glance, I thought I'd see how it might work.

Ahh ok. So first off to balance the steps between each dice your going to have to modify the boost/setback dice. D4 becomes your base dice,

Base Positive (d4): 2 blank sides, 1 side "S", 1 side "SA"

Base Negative (d4): 2 Blank sides, 1 side "T", 1 side "FT"

Boost : change 1 blank side to a "SA"

Setback: change 1 blank side to a "FT"

D10 is positioned between d8 & d12... Obviously. Keep the triumph and despair on the d12 only

The reason you will need to modify the Boost/Setback dice is because they where never intended to be a dice that's upgraded. They are balanced to allow 5 or 6 in a pool without massively skewing the results. If left as they are then upgrading a D6 to D8 will have a significant effect on the results, too much of a step up.