The way you have pictured your Anubias is fine. As Digsy mentioned, I would personally attach it to driftwood (i.e. with black cotton thread or fishing line) rather than plant it into the substrate. However, as long as the rhizome remains above the substrate, you should be fine.
The way I attach annubias to driftwood is that I cut ALL the roots off as close as I cane to the ryzone. I the place it on the driftwood and tie it or staple it in place.
The roots "usually" start to grow back fairly quick. Some of them are obviously "not" attached to the wood. Some of them though, you can plainly see are attached. they look like the are "hugging" right allong the contours of the wood.
Once you see some of those roots, you can remove the thread or staples.