The Relationship spread is a modern layout of unrecorded authorship, and it raises a question of practice that the other spreads in this atlas do not.
Provenance
Like most spreads in general circulation, this one has no traceable first appearance and no named author. Seven-card relationship layouts appear across twentieth-century tarot handbooks with the positions varying between books. The atlas records the layout in use here and states the authorship as unknown rather than supplying a name.
The second position is a person
One position in this spread stands for someone who is not present, has not asked for a reading, and has not agreed to be read about. Working readers differ on how to handle that, and the range of positions is worth knowing rather than being told which is correct.
The most common practical convention is that the position describes the querent's side of the connection and what they are able to see of the other person, rather than the other person's private thoughts. Readers who work that way say so at the start of the reading. Others decline third-party questions altogether.
Why the atlas records the caution
This is a living practice with an ethical dimension that its practitioners discuss openly, and describing the layout without it would leave out something the tradition itself considers part of the technique. The atlas describes the practice; it does not instruct anyone in it.