That is very interesting. my experience with Spiral Welded pipe has ben SAW only. 4.0 MM GMAW would be interesting to see.
The transfer mode is best established by observation as opposed to the theory since you are there to observe what is happening. An oscilloscope or even high-speed video could be used to observe what is happening if you are undecided between short circuit and globular. Because you are using 30% CO2 only then theoretically, spray does not occur. I, however, have never used 4MM GMAW so I am only speaking from knowledge of information read. I have observed metal transfer that looked like, sounded like, and welded like spray using 75/25 Argon/Co2.
Spray is pretty obvious when it occurs also.
A paper on the subject of transfer mode sensing can be read at
http://files.aws.org/wj/supplement/WJ_1991_04_s91.pdf which may lead you to more information other than opinions.
In my mind, your options are globular and short circuit if you are sticking to accepted "theory" but verification using theory is not as strong as verification using observation. There are variations of our standard "textbook" modes and many research papers on the process.
If you are trying to use the transfer mode as a basis for qualifcation ranges related to thickness, I strongly suggest verification of suitability on all thicknesses to be welded. I know that could be an expensive process on a spiral weld setup but for straight seams, it could be a little easer.