HCSR04

What distance is it reading in this situation?
I know that this module emits 8 signals, but are they at the same direction (straight out from the HC-SR04)?

Whichever is shorter. This assumes that the bottom of the overhanging object is within around 15degrees off the normal from the sensor.

Easiest way to find out is to use a narrow movable object and wave it about. Ruler would probably work.