Thank you Shane. May I recall that in my initial posting, I mentioned that this test is for a WPS and it is under AWS D1.1 not, ASME IX. If you will note, position is not an essential variable in ASME IX but it is in AWS D1.1 Meaning, a qualification test for 4G only covers OH. But I also said, the welder will be qualified through this WPS test. So that means the welder will be qualified for F, OH as per table 4.9. That pretty much makes sense because as one respondent here mentions, he or she wouldn't allow the welder to "move" the piece. If that is the case, the welder would have to complete the back weld that is regarded as a backing in the 1G position or F for Flat. Even in ASME IX, performance qualification test in 4G position only qualifies the welder for F, O not "all positions".
IMO, a WPS test that takes into consideration the orientation of the weld joint will be designed to test just that. I have never seen nor have I come across any customer that require WPS test be conducted for other than standard single-V-groove. That means, no double-V-groove nor double-U-groove or other special weld profiles. In my example, it will be just the standard single-V-groove with a root face and opening meant for full penetration. The back weld will be limited to a single pass to provide capping on the other side. If you will recall Figure 4.14 - Reduced-Section Tension Specimen, all excess weld will be machined away. Even for the Bend Specimens again, the weld reinforcement and backing shall be removed flush with the surface of the specimen. That means the back pass doesn't figure much in the mechanical tests. I would say, if the test piece is 1 in. and over, the WPS test conducted without the piece being "moved" should be qualified for "unlimited thickness".