Ok, @colintrainor 's response to our discussion here:
I've already looked at ExpA values. I see the discussion over at fightingcock, I don't want to weight the passes so that earlier passes achieve less. By doing this we effectively arrive at the Shots / Key Pass stats where a player needs to be frontline attack to score highly on that scale. This way deep lying players can (in theory) score highly, and if enough passes go through the deep lying midfielder in the moves then he should get credit for that. Not water down his impact. And I deliberately didn't use ExpG values because then the debate becomes around the specific ExpG model, which takes away from the actual concept at hand.
So, there's the why of it.
I've already looked at ExpA values. I see the discussion over at fightingcock, I don't want to weight the passes so that earlier passes achieve less. By doing this we effectively arrive at the Shots / Key Pass stats where a player needs to be frontline attack to score highly on that scale. This way deep lying players can (in theory) score highly, and if enough passes go through the deep lying midfielder in the moves then he should get credit for that. Not water down his impact. And I deliberately didn't use ExpG values because then the debate becomes around the specific ExpG model, which takes away from the actual concept at hand.
So, there's the why of it.