Per: https://www.reddit.com/r/RTLSDR/comments/9ahdzc/modification_of_wifi_grid_antenna_to_make_it_work/

A 2.5cm spacer is required.  I have 4mm nylon spacers on hand.  After drilling the spacers out to slider over a 8-32 nylon screw, physically works to offset the secondary reflector.  I have not yet tested