Wrong sign in xshift of node in with reversed arrow?

[TorbjornT]

This is in reference to https://tex.stackexchange.com/questions/377299/tikz-feynman-asymmetry-between-particle-and-antiparticle-lines/410367#410367

Should the xshift of the node in with reversed arrow have the opposite sign as that in with arrow? Currently both with arrow:

tikz-feynman/tikzfeynman.keys.code.tex

Line 295 in 8d18590

xshift=-0.5mm,

and with reversed arrow:

tikz-feynman/tikzfeynman.keys.code.tex

Line 313 in 8d18590

xshift=-0.5mm,

do xshift=-0.5mm, causing the asymmetry mentioned in that TeX.SX post.

[losmaxos]

Hi,
seems like this is due to TikZ not placing the isoscele triangles "half-width-center" at the lines' center,
but rather at their center of gravity or something like this. This roughly needs an xshift of 1/6 the arrows width, see below.
In addition to the symmetry desired by the original poster (arrows point in SAME direction), we also want symmetry when we have a fermion and an antifermion right above each other, with the arrows pointing in OPPOSITE directions.

What worked for me was using for with arrow:

      xshift= -0.166666*arrow width,

and for reversed arrow:

      xshift= 0.166666*arrow width,