creating a dynamic set of users on a criteria based on strings contained inside an attribute bound to users

in resources i created an attribute of type string (indexed)

i populated that attribute in all the users.

now i want to create a set based on the value inside that attribute bound to users. But the only search criteria i see is 

but i want that there should be 'contains' feature also so that i can search and combine parts of this string to search more specifically for making my dynamic set. when i use the search for users based on this attribute in search i see the 'contains' feature but its absent only while making sets.