I had always heard of chain suck being when the chain is lifted up into the gap between the stay and the rings by either dirty, nicked or worn rings: hence the wide array of bolt-on devices that were so popular in the 90's If your chain is just dropping off the inside, adjusting the limit screw and/or getting a high flanged, narrow BB spacer to keep it out of the cranks should help solve your problem. I had my chain fall off and into the gap between my little ring and the bb shell one time on a night ride- major pain in the a$$ to fix in the dark.

G