As for me (and my interpretation of the OOK, at any rate probably "incorrect", but don't mind) if the center card (principal) is surrounded by cards (the modifiers) that are completely opposite elementally, the modifiers well-dignify the principal.
7 of Cups ~ Ace of Wands ~ 9 of Wands
Ace is dignified
BUT if the 9 of Wands were a sword it would not be:
7 of Cups ~ Ace of Wands ~ 9 of Swords
Ace not dignified
[Now switching the Swords back to an Ace...]
I also chainlink them together, like this:
7 of Cups ~ Ace of Wands ~ 9 of Wands ~ 6 of Cups
and consider the Ace of Wands and the 9 of Wands dignified.
Now, if a Disk followed the 6 of Cups,
7 of Cups ~ Ace of Wands ~ 9 of Wands ~ 6 of Cups ~10 of Disks
then I would consider each card between opposite elements as dignified:
9 of Wands (between fire & water)
My tarot-reading buddy ("puckinfl" who helped me develop and with whom I regularly practiced this system/interpretation from the not-so-clear instructions from Mathers etal) used to take it a step further, using the masculine/feminie dichotomy to "slightly dignify" cards, but that was too tall an order for my feeble brain:
9 of Wands (masc.) and 10 of Disks (fem.) =
6 of Cups, "slightly dignified"
OR conversely
7 of Cups ~ Ace of Wands ~ 9 of Wands ~ 6 of Cups ~10 of Disks ~ 6 of Disks
6 of Cups (fem.) and 6 of Disks (fem.) =
10 of Disks NOT dignified at all, although he would say not "ill-dignifed" either: Neutral
Again, his method of taking the elemental dignities a step further always stymied me so I didn't use them this way; only considering the elemental opposites (i.e. "enemies") when dignifying.
I seem to remember his philosophy "the enemy of my enemy is my friend." Again, too confusing so I stick to just the opposing elements when choosing.
Great topic! Thanks for sharing