jouou

There's an entire 淡交テキスト about it (I 2009)
The old book explains that things related to the making of tea don't belong on the top shelf. But you can display 板文庫, and 硯(箱), or single-flower vase, 炭斗, 巻物 or a 香炉 on it.
My thinking is that this is linking it to a pre-詫び time when there were writing desks in the room.
On the lower shelf, there's a 棗, and it's there pretty much for the entire 茶事.
Used for 炉 only, duh, because where would you put the 風炉?

香合 and feather are displayed in the front left corner of the top board (as with the 台子) in the 八 shape.

During 中立, open the right sliding door and pull out the 水指. The 茶入 waits in the middle of the 棚 (akin to 山里).
The 仕覆 lives in the front left corner of the bottom shelf — that's different from the 台子!
You open the huge ass lid normally on the top handle, and rest it against the 棚 itself, peeking out about half its size 🤯
You'd like (I assume) to put the 柄杓 and 蓋置 in the left compartment, but alas, the 水指 is still out (and needs to be until you 水次 it). So you place them temporarily on the lower board:
- either with the 柄杓 straight near the left edge and the 蓋置 in the middle to its right; (淡交テキスト only)
- or with the 柄杓 at a slight angle and the 蓋置 to its left, in the front left corner. (both)
Sit in the middle of the 棚 with the 水次 (that's the old book, 淡交テキスト says to sit in front of the 水指), pour and put the 水指 away, then open the left door. Put in the 柄杓 with RL, at an angle facing away from the guest with the cup facing downwards (old book, テキスト puts up), and the 蓋置 with RLR to its R.

At the beginning of the 点前, you enter with 茶碗 and then open the 水指 door and get it out. Then you take the 棗 and put the 茶碗 in its right place, that is, in the middle of the 棚.
Same dance with the 水次 and the
After 拝見, put the 棗 back on the lower board, putting the 茶杓 in its front right corner temporarily.

Arrange 茶碗 and 棗, then put 柄杓 and 蓋置 in their temporary position.
Put 茶碗・茶器 onto the middle shelf, in the middle
Come in with the 水次, and put your 帛紗 on the 水指 lid (if lacquered) before putting it back in. Then put the 柄杓・蓋置 in the left compartment.

In the 淡交テキスト above they use this with a 筒茶碗 for 薄茶 (without doing 絞り茶巾!), and use the 蓋置 with the 3 fellas, as well as an all black 棗.