I've read a good deal of discussion on the value of the pitch calling (PC) rating on these boards, often correlating a certain jump in that rating with a corresponding decline in ERA (I think 0.25 runs per 10 points of PC is the one I've seen most often).  My question on the rating is a bit different but related to the studies that have pointed to that indicator.

Specifically, do we believe that PC has a constant effect (with normal sample variance) across all types of pitchers or if it is more valuable in combination with certain types of pitchers.  Thinking about this in terms of real baseball is simple (A hard thrower with 10 years of ML experience and 2 pitches is less likely to rely on a catcher who can call a great game than a 22-year-old junk baller with 5 pitches to choose from) but this means little to nothing in relation to HBD.  Do we think different pitchers benefit differently from PC or that it's essentially an independent variable that gets thrown into the secret sauce in the same quantity regardless of pitcher?

Same variable in the secret sauce regardless of pitcher.

I think they have stated it is simply a modifier of some sort.
So in that regard it would be constant regardless of pitcher.

Unless it modifies based on a % bump, right?  Is this plausible? So then the pitchers with the higher ratings would get more of a benefit.

I have always wondered if pitch-calling really correlated to the pitcher's array of pitches. For example, if my starter has four pitches: 75/72/69/66 can I start a catcher with 40 PC and not be hurt too much? Conversely, if my starter is an 85/81/52/38 guy, do a go with the catcher with the 80 PC? While I would like to think this type of logic might be used in the sim, I suspect it is a simple modifier applied across all pitchers equally.

I always use catchers with high PC ratings, and tend to get my pitchers at a discount, because I don't put a lot of emphasis on high splits. I look more at the individual pitches. And I think the high PC rating helps even more if the ratings of the pitches are not in successive order, i.e. 75-79-62-66.