Isn't it a messy business ?
Isn't it a messy business, Master Therion, to mix a 5-element system with a 4-element system ?
For exemple, consider the following paragraph quoted from your Book of Thoth :
"The Knight of Disks represents the fiery part of Earth, and refers in particular to the phenomena of mountains, earthquakes, and gravitation; but it also represents the activity of Earth regarded as the producer of Life. (...) He rides through the fertile land; even the distant hills are cultivated fields. (...) In the Yi King, the fiery part of Earth is represented by the 62nd hexagram, Hsiao Kwo. (...) The character described by this card is therefore exceeding complex, yet admirably well-knit ; but its dangers are indicated by the symbols of Luna and the bird."
If we take a look at the 62nd hexagram, we see the trigram Thunder standing at the top of the trigram Mountain ; in terms of the 5-element system, it's made of a Wood controlling an Earth. Problematique, non ? Yes, our imagination is certainly inflamed, if the fiery part of Earth might have something to do with Earth being overpowered by Wood. And, indeed, why not think of the universe as one big alchemical pot !!!
However, when the card involves only one single element, it poses "almost" no problem :
"The Princess of Disk, the last of the Court cards, represents the earthy part of Earth. She is consequently on the brink of transfiguration. (...) In the Yi King, the earthy part of Earth is represented by the 52nd hexagram, Kan. The meaning is "a mountain" ; of how sublime a significance is this Chinese doctrine of Balance, and how closely congruous with that of the Holy Qabalah !"
Let's take a look at the 52nd hexagram : a Mountain over a Mountain, hence Earth over Earth. The element being pure, no problem... as far as I am concerned... What about you, Master Therion ?
PS. 5-element system : Metal->Wood->Earth->Water->Fire->Metal...
4-element system : Earth<->Wind ; Water<->Fire