Hi,
I went from PSTricks to Metapost (Metafun) gradually. For positioning arrows
between two values in an array of variations, I used a command like this \
ncline {A}{B}, which avoids fumbling.
Can we do the same with Metapost ?
The idea would be to convert the value into a path or an image, much like in
the code below.

\starttext
\startMPcode
u:=1cm ;
path p, q ;
p=fullsquare scaled u ;
q=fullsquare scaled u shifted (4u,-2u) ;
draw p ;
draw q ;
drawarrow center p--center q ;
label(btex $5$ etex,center p) ;
label(btex $-2 $ etex,center q) ;
\stopMPcode
\stoptext

Best regards,
Fabrice