What's the difference between the half lotus and the perfect pose?

[Something Funny]

I am reading the Kriya Secrets Revealed book, and the first lesson is about choosing a sitting pose. 

Among others, there are half lotus and perfect pose siddhasana. However, they seem pretty much identical to me. What's the difference between them?

[Oppositionless]

It appears that perfect pose only the foot is on top of the other foot, half lotus the whole leg is on top of the other . That's crazy bc I thought perfect pose both feet were on the ground . I'm still gonna do it that way when I want extra grounding / stretch lol.