Anyone else having 4 player only bracket as well?

Technically a even less, the odds of landing in the 4 person group are lower than for all the 8 person groups.

(4999 * 8) + 4 = 39,996 (available GAC spots across all groups in the division)

4 of those spots are in the small group so

4/39996 * 100 = 0.01%. ?

Of course depends heavily on how many groups there actually are.