Adjusted Pickup Method – Shift Factor

I have been looking into the adjusted pickup method and associated shift factors used when multiple source bus configurations are being coordinated [ex. parallel generator systems two or more] and was hoping someone could point me to an IEEE standard or some industry articles on this to better understand this on shifting TCC’s around a specific location or device. On one example where two different sized generators were modeled it shifted the smaller units beyond the TCC of the larger unit indicating a longer trip time for that device for a downstream fault condition. It looks that the shift factor calculation looks at the generator current to the fault / the fault current at the location specified, assuming that larger gen breaker sees more current and trips faster than the smaller unit, this is what I am seeing and was looking for some backup information but searching around it appeared the information was pretty scarce and was hoping someone could point me toward some. THANKS. READ MORE