Aha! I found data sheets on the two fans I mentioned.
The one I am using generates a paltry 0.03 psi of vacuum.
The actual air assist part generates a fair bit more, closer to 0.05 psi:
https://www.mouser.com/datasheet/2/632/THA40x40x20-515731.pdf
Now to go see if I can find a better option.