Assigning (missing?) effects to the pad

Controller: DDJ-400

OS: Mojave 10.14.6

Rekordbox: 6.4.2

I'm trying to assign low cut echo to my effects pad, but it doesn't seem to be an option.

I searched the manual (including pp 111, 119, 120, 160-71) + this site + rekordbox and didn't see an explanation. Is that the expected way certain effects work? Some only work from the panel and the Release FX button?

Available in the panel:

Available in the pad remapping panel:

(The effect(s) are also missing from the sound color and release FX submenus)