DCID = Distinct by ConnID. The Formula identifies a Connection ID. If webchat has a ConnID and you can implement DCID onto the Stat, it should count multiple pass-through Interactions only once. If webchat (logs) do not contain a ConnID, then DCID is invalid for that interaction type.
Multimedia interactions don’t have interaction I’d as their “natural” property - it just temporary generated for processing usually by URS. Different runs of strategy for the same interaction for example easily can have different connection id.