This discussion is getting convoluted with new, additional, and changing conditions as the thread drags out.
The bottom line; if it is unclear just what the weld joint looks like, provide a sketch detailing the actual conditions and details. Why should we guess what is being welded? Provide all the facts and details upfront. This isn't Paul Harvey's radio spot where we have to wait until after the commercial to hear the rest of the story. This is the second thread I've read today where the individual posting the question has to be queried to provide more detail.
Preheat is based on the thickness of the thicker member and whether hydrogen controls are in place. If the detail requires the thicker member to be machined to reduce the thickness to the same or similar thickness as the thinner member, preheat is still based on the full thickness of the thicker member. That would be the case unless the reduced thickness extends a multiple of the reduced thickness, i.e., several inches. My position is based on the fact that the thicker section is still a heat sink unless the reduced thickness extends for a distance that ensures the heat sink effect isn't a factor.
If the case is "special,” show us the special conditions so we can provide a reasonable response.
What I like about forums such as ours is if you don't like the answers recieved, feel free to visit other forums. Surely, sooner or later the response sought will be found. The value of the infomation provided is often worth just what you pay for it. It isn't worth much if it cost nothing, but it is worth a million dollars if that is what you paid. The response may not be any more valid, but you might feel more comfortable with the answer if it is expensive. If the information is wrong, it will be expensive by the time the project is completed.
Inspectors, under the auspices of D1.1, can be in-house inspectors that have no formal training, little experience, and are still assigned the task of representing the fabricator on inspection matters. The in-house inspector may not be certified or may be certified by his employer in accordance with AWS B5.2 or ASNT SNT-TC-1A. The training provided is whatever the employer feels is adequate for the tasks that need to be performed. If the inspector is certified by AWS, i.e., a CWI, there is no assurance he/she has a working knowledge of D1.1 or that a copy of D1.1 is available to reference.
One of the first questions I ask when performing as a third party inspector is, "What is the color of the cover of D1.1?" It is surprising how many times the response is a blank stare and "I don't know."
You cannot inspect the work properly without copies of the applicable standards. Few of us have the intellect or memory to perform our job without referring to the appropriate standards. I typically carry a copy of the AISC Steel Construction Manual, AWS D1.1, and my ASTM standards when I inspect structural steel. My hat is off to anyone that has the mental capacity to have all that information stored in their memory and do not need to reference those standards when performing structural steel inspections.
It sounds as if this particular inspector is so smart he doesn't need to review the requirements of D1.1. He may be familar with NAVSEA TP278 which is not as conservative as D1.1. The problem is that the current project must comply with D1.1. This is another case of what was done on the last job has little to do with the current project.
As I've said before, "10% of the people excel at their jobs, 80% perform adequately, and 10% should find different employment." I usual do my damn best to make sure I don’t fall into the latter category.
Happy Holidays Fellas!
Best regards - Al
I agree with Brent, using a heavier electrode will help you run a few extra passes before hitting the upper interpass limit of 400F because your travel speeds will be faster and you'll be putting more material in the joint. I didn't see in the questions/replies where that 400F came from, so I'm assuming the WPS was written showing a 400F upper limit. 
You Rock, Al
