attach does not seem to be working properly

[kands-code]

I'm new to typst and I've been learning how to write with typst, But in learning to use attach encountered the following situation, what is the reason?

code here:

$
  3 attach(M, t: arrow.long, br: 1, tr: 2) + 2 = 10 \
  12 = attach(V, t: arrow.long, br: 1) + 3
$

Many thanks.

[kands-code]

If I provide both tr and br, such as the following code, attach seems to work

$
  3 attach(M, t: arrow.long, br: 1, tr: 2) + 2 = 10 \
  12 = attach(V, t: arrow.long, tr: "", br: 1) + 3
$

[kands-code]

Oh, I think I know, it's described in the document:

The top attachment, smartly positioned at top-right or above the base.

You can wrap the base in limits() or scripts() to override the smart positioning.

But for me, it's not smart at all.