I came across the concept of 'V mixing' (my own term for this) via multiple sources. The most significant was my hands-on experience of using the Waves plug-in Vitamin, a multi-band effect that allows for width control of adjustable frequency bands. A screenshot of the plug-in is shown below:
Another is from what I noticed listening to music at home, how mixing engineers nowadays pan different instruments. As the diagram below (left) illustrates, instruments with significantly more low-frequency content tend to be mixed in the center position, or mono, and instruments that tend to higher frequencies are panned more extremely. Notice the kick, bass and snare in the middle, and the guitars, violins and cymbals spread throughout the stereo field.
The combination of frequency width control (Vitamin) and panning will give you 'V mixing.' The right diagram shows, very basically, how a spectrum would look in a stereo/frequency field. Lower frequencies will range from mono to low width, and higher frequencies will feature more width.
Contrary to what I believed, the researchers at AES found that the theory that higher frequency content is mixed wider, was false:
"Another assumption that was proven false was that the higher the frequency content the wider the pan position might be...It seems that other than low-frequency content (be-low 200Hz) everything is open to wide panning"
- Source: Pedro Pestana and Joshua D. Reiss, Intelligent audio production strategies informed by best practices, 2014. pg. 4. (Click HERE)
Since the AES researchers mostly used 'top100 charts' music, which I stay far away from, I find it likely that 'my kind of music' (metal, rock, blues) differs from popular music (and any denomination of it: HipHop, etc.) in its mixing aesthetic/s.
"In a heavy rock piece with distorted guitars, depth is key. The sense of space is important not only for creating a soundstage, but also to create a sense of pressure for the aggressive guitars. To help reinforce the sense of depth, a mastering engineer can apply Mid/Side EQ and boost the high shelf on the sides slightly. This will increase the sense of space without altering the most important centered sounds, such as the vocal."
- Source: https://www.izotope.com/en/community/blog/tips-tutorials/2014/06/mastering-for-different-musical-genres/
Song: Original composition called 'Fragment.'