I do love this set of pictures from Zen Mountain Monastery. I think they can really be helpful. I might add in my circles the “quarter lotus” is usually called the half ass lotus (lovingly, of course…).
I should also note himself (the good one) added one can also “sit” walking, standing up and lying down.
If you hold the various absolutist assertions lightly, this video provides a pretty good set of instructions on getting into the posture.
Also the video is a bit fast on the interior parts…
So, for a little more on where to tuck that brain, you might look here.