5120 is value specific to OS, but all GM OBD2 VPW PCMs should have it the same way.
Cylinder volume is the value in calibration {B0104 - Cylinder Volume} and it should match the engine cylinder...

OK, I can see it's 2088 OS.

X/5120 = g*K/kPa
(X/0.1767711646826163)/Y = VE %

X - raw VE value,
Y - cylinder volume in cc

What OS/car are we talking about? The sreenshot is too bad to see that.