I'm also trying to find answers myself. I have found a number of references to horizontal draining and wet vents. In an answer to someone's question regarding a shower base, NHMASTER, answered that a 2" horizontal drain could be run 6' before needing a vent. Does this still apply to system that is supposedly wet vented?
If so, I'm feeling pinched as I would like to move my drain 15" further away from the current location. How can I prove to the plumbing inspector that I'm still within 6' if all the plumbing is buried in the slab?