Two camera VR setup - how to make a crosshair?

I'm using two normal unity cameras (no VR plugins, just the internal VR) and everything is working fine in the GearVR.
Now I want to add a crosshair dot inside the cameras. When I attach the a sprite to the two cameras I see my crosshair in the GearVR but its not in the correct spot (too far appart). What can I do to position the crosshair correctly?

My hierachy:
empty-left
--camLeft (rendering layer left)
----Canvas
------Image

empty-right
--camRight (rendering layer right)
----Canvas...

Two camera VR setup - how to make a crosshair?