It's the of 香合; but it's also a bit of a jack-of-all-trades. You could use it for a 香合 that you received from someone special (「ごゆいしょ。。。」); but also for a famed one (「ごでんらい。。。」). Because of that, it might be a suitable 手前 for 行の行 (Miya 24; see below).

Hiromi (pre-23), however, explained that it will be very tight to do with a , and even if it were possible, it would be a pretty silly idea, since you want to spotlight the 香合 and not have any distractions. In 表千家, still, they do it on the .

👋 Note the spelling of 手前: For charcoal, you write 「手前」, for tea 「点前」.

手前

🤓 This is the only situation in 子習 where you put something on 環付; which supports my idea that it can also be used for famed 香合!

台子

🫸 This is a conjecture of Miya and me.