There are two problems that I didn’t know how to fix.

1) The line connects to the box including the subscript or superscript, not just to the e.
2) I cannot make multiple connections to a single object, like the e^\mu in the center. If I try to connect top and bottom, I get no connections anywhere in the entire document.

The code for the formulas is:

\startformula
  % Each \connectboxanchors works alone, but both together make trouble:
    \connectboxanchors[top][top]{X}{Y}
    %\connectboxanchors[bottom][bottom]{Y}{Z}
  \mathboxanchored{X}{e}_\alpha \mathboxanchored{Y}{e}^\mu \mathboxanchored{Z}{e}_{\dot\beta}
    = \textfrac{1}{\sqrt{2}}\sigma_{\alpha\dot\beta}^\mu
\stopformula

I added code to turn the arrow produced by \connectboxanchors into my contraction overlay, but that doesn’t affect these issues.

> in your example we need a way to anchor on just the 'e' right? or do you want it on the e + super/subscript?

Yes, we only need to anchor to e. 

Thanks!
Gavin