Treat each supply and load as separate. Imagine changing the labels on that diagram so it says "Arduino" instead of "sensor1" and "power supply" instead of "sensor2". That doesn't change the wires going to the ground point.
It doesn't really matter how 'close' the supplies are. The power's really coming from a hydroelectric dam hundreds of km away, isn't it? What does matter is having a single point that every component can agree upon to measure "ground" from. One supply or one sensor may have a long wire going to that point.