that is strange. OmniFocus documentation (see the quote in my post) says that it should be prefixed with /task and /project
but @sylumer has a working omnifocus so I think the blog quote my pe misleading.
@zeltak have you posted a question on the Omnifocus Community or to Omnifocus themselves. the price of the app should give them time to a better documentation as I found on the web.
But I am shure they love to help!
Something like https://culturedcode.com/things/support/articles/2803573/