I do not completely understand your issue, please elaborate further.
Do you want to have the ARView in full size but with a navigation partially in front of it?
Do you want to have the navigation/tab bar side by side with the ARView?
Still haven't heard back from you... This is one of the last problems on my list of todos and it's really holding me back.
Neither of those links really helped me... The first one is about adding a UI on top of an already separated ar-view, and the second one is for Xcode (although it sounds along the line of what I'm looking for).
Can you please further explain how I'd go about doing this in a Cordova (technically Ionic, but Cordova should suffice) project?