I think they drop WAY more frequently from LOL X.. anything higher and they are much less frequent. Probably because there are more rewards which will drop above X so the Lilith Frags are just 1 thing among several and RNG doesn't pick them to drop as often. In addition the SOT cost above X means you are getting less chances for frags to drop.
They are dropping.. farming LOL 14 today.. and I've picked up only 85.. which isn't much, but it's something. If you want more Lilith frags, your'e better off farming LOL X.