Question about the part probabilities

[Bingoang]

Hi, taconite!
I really interesting about your paper, but I have a question about the part probabilities:
For each query point p, we calculate a probability simplex p_hat(shape: B×24×N) to judge which part of the SMPL the query point p belongs to. There are totally 24 parts in SMPL. Why is the shape of probability simplex p_hat not B×(24+2)×N? What if the query point p does not belong to any part of the SMPL body (e.g. point p is inside or outside the surface)?
I cannot figured it out, and I really hope you can answer me. Thanks in advance~