How do U+2571..U+2573 connect?

[Manuel Strehl]

Hi,

if you look at the Box Drawing block, e.g., 
https://codepoints.net/box_drawing, every character goes through the 
middle of the edges of an imagined rectangle around the glyph. That is, 
apart from U+2571, U+2572 and U+2573, the diagonal lines. Those touch 
exclusively the corners of said rectangle.

I fail to imagine how these three characters could ever attach to any of 
the other characters in this block. Are they not meant to do that or am 
I missing a trick here?

Thanks for any pointers!

Cheers,
Manuel

PS: This question was triggered by this reddit post: 
https://www.reddit.com/r/Unicode/comments/127y7dn/looking_for_box_drawing_characters/