I have to wonder if you truly believe it is using the same settings if you don't share the settings or if you actually mean "similar" settings.
For instance, it is possible to use the same "VOIP Carrier" without using the same entry under Admin->Carriers in Vicidial by having two "Carriers" pointing to the same provider. Then the settings would be different, resulting easily in a different call quality.
So ... how identical are these campaigns? Did you "copy campaign" from one to the other? Or are you summarizing in a way to mean you tried to make them similar?
Are these campaigns on the Same Server? (also easy to have completely different results ... obviously, and not necessarily related to the hardware or software in any way).