> As far as I can see:
>
> Sekihara et al. 2004 calls it optimal
> Fieldtrip just calculates this when the fixedori parameter is True (but they say "compute the leadfield for the optimal dipole orientation" in the comments)
> Nutmeg calculates this orientation by default, so no parameter is used and no comments are made

I see that you did your homework :)

you make me doubt about the pca naming. I'd like later to have pca in
MNE, dSPM etc. but it would do things differently (do SVDs on source
time courses).

maybe optimal is the most well accepted term after all…

let me know if you have a better option.