Seperator plates, Transgo vs stock

I was comparing some seperator plates today, and got to wondering why the replacement ones from Transgo have one hole (picture) that's much smaller than the stock ones I have on hand. I was hoping somebody could clarify A) which circuit this hole is part of, and B) why they decided to reduce it's diameter so drastically. Factory is .300" (A500, 46RH and 46RE ones I have), their early VB w/o boost tube plate is .108", and their later VB w/ boost tube plate is .040"
Thanks, Karlin.

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