Alignment of anchored frames

Issue: In a one column text frame with a side head, I'd like to align an anchored frame at the top of (and within!) the column

1. Create a blank document.
2. On the body page, change the text frame properties: Add a side head.
3. Type some lines.
4. Insert an anchored frame.
   • Anchoring Position: Below Current Line
   • Alignment: Left
   • No Cropping, no Floating

Everything works as expected:

Now change the Anchoring Position of the frame to At Top of Column:

The frame is placed at the top. That's fine.

But the frame spans the column and the side head. That's not what I want and, btw, not what I expected.

Now change the Number of Columns to 2:

Again, everything works as expected: The frame is at the top of the column and it is within the column only.

I'd like to have this (The image below is created using a graphics tool.):

• One column
• A side head
• Anchored frame at the top of the column
• Anchored frame within the column only

How do I get it in FM?