Oculus GO controller (or canvas?) off center when selecting

I'm implementing the use of the Oculus GO controller (https://developer.oculus.com/blog/easy-controller-selection/) into an existing project that uses a curved canvas. It's almost working EXCEPT when I point directly at the button it doesn't work, but if I point just above the button the item is selected.

In other words, something is is off target but I don't know where to focus my attention to fix this. Any ideas?