So, Arsenal lists four strains of FAB: I, II, II-b, and III. My copy of Street Magic (the FanPro printing with the blue cover) only describes I, II, and III. What's II-b? How does it differ from regular FAB II?

Fab II is used in tanks to make an astral barrier

FAB-IIb is suspended in a liquid which is dispersed in the air. This does not form an astral barrier; it prevents astral movement
through the mist its attached to no faster than 100 meters per Combat Turn
and increases the threshold for Assensing Tests by 2 when looking
through the mist. It lasts for approximately 4 Combat Turns (less
in windy areas, longer in confined areas at the gamemaster’s discretion

Increases the threshold for Assensing? Is that from the orange version of Street Magic? My book says it applies a -2 penalty to Assensing.

pg 64-65 of the Arsenal Book actually.

Aha! That makes it exactly what I need. Thanks!