That thread actually had a couple of separate pieces of relevance in the query. The check for `__Group_X_xxxx’ settings only applies to Manual (and possibly Server-Based) groups.
For Automatic Groups you have to check the headers of relevant fixlets -
(unique values of it) of ((values of headers "subject" of relevant fixlets whose (value of header "X-Fixlet-Type" of it = "ComputerGroup") of sites)