That's right. Just as "contains 192" does not work, this makes it useless in this case.
192.0.0.0/8 would match "192" only in the start of the address, which is what OP wants I guess.
If we have two addresses: 192.168.1.2 and 123.192.11.2, how would I match these two with one rule containig 192? No way. If I write two rules, they are linked with AND and I would not be able to write several conditions to match "192" in the four possible parts of the address.
This leads us to my problem with "OR"
.
Anyway, this would not be easy even if I had the chance to write 4 conditions because what this would require is something like *.192.*.*