OK, that makes things a little clearer for me. As it turns out, I've spent quite a bit of time recently with that atlas. It is distributed with both surface and volumetric versions with probabilistic maps too in both formats. While it might not be obvious how to use the surface versions, I think that version is better in terms of contiguity and mapping to the MNI 2009c template or to each individual subject. PM me if you would like to chat about it, and we can set up a Zoom meeting to discuss.