Fucking hell. They've nerfed Expert Lilims to 3 Grails every time. Meanwhile, Standard is still at 1-3 Grails.
Back to Standard farming it is then.
EDIT: Okay, it is possible to get 4 Grails from Expert. Gotten that twice in 10 kills.
15/2 = 7.5 AP/Grail from Standard
25/3.2 = 7.8 AP/Grail from Expert
Considering the HP difference between the two, you're probably best off just farming Standard.