What you are using should work. I would perhaps verify that the value is set correctly. You should be able to inspect the omtrdc network call in the network panel and look for context/address/referringUrl for the Previous page value.
You can theoretically set as Audience "Traffic Source" > Referring Landing Page: URL. However, I have to say that I had already tried this twice - and had rather bad experiences with it.
What you are using should work. I would perhaps verify that the value is set correctly. You should be able to inspect the omtrdc network call in the network panel and look for context/address/referringUrl for the Previous page value.