All things considered, it really seems quite arbitrary as levels of interaction/thread visibility are spread rather evenly.Was in on the list:
player/post count placement/alignment/interaction level
Michelle 4 - t - interacted with
WWA 1 - ? - was around with
LF 12 - W - was around with
Nut 3 - ? - was around with
DM 13 - t - interacted with
Rondo 8 - t - interacted with
Cape 7 - 3p - interacted with
Was not on the list but was in thread at the same time as Brad:
MR 9 - ? - Interacted with
Creature 5 - t - Interacted with
Me 12 - t - was around with
Sabi 2 - t - was around with
Alison 11 - t - was around with
Dizzy 10 - t - Interacted with
Was not on the list nor was in the thread at the same time as Brad:
Nook - t - 14
Davos - ? - 16
Sabi who was rather active, didn't get interacted with or put on the list.
Nook/Davos seems like they were forgotten about entirely.
Brad did prefer more active players and players who were more active in the thread at this time who they interacted with with outliers to this rule being Nut/WWA. The fact that MR was interacted with but wasn't put on the list is of note, but I can't tell if it's the same behavior as seen with Dizzy/Creature who both had varying levels of activity.
Without knowing Brad's spew/antispew patterns, I think it boils down to the WIFOM of 'would the teammate be included or not'