I think at first the triggering factor needs to be changed to "any damage received" and go from there to see if the trigger percentage needs be changed. With VR, Ancient is a 17% trigger chance but as Rhap mentioned, it doesn't proc off surge and there's very few mobs with "spell damage" that it'll proc off of anyway.
Potency aside, the damage proc on it, Shock of Sound, could definitely use some help as well. Unfortunately due to the very low trigger chance of the buff itself I don't have a lot of data on this, but the times I did see it hit, it was very low and negligible. If the 3 trigger limit must stay in affect, then the damage should be increased by double or triple. However the best solution would be to just eliminate the trigger limit and allow it to proc off of any damage received as the spell itself states.