How to correctly position optical sensors in applications?

For proper and reliable operation of applications with optical sensors, it is necessary not only to choose the right sensors, but also to mount them correctly and orient them towards the object we want to detect.

See the following figures for examples of correct and incorrect sensor-to-target orientation as certain placements may pose problems for sensing some targets. 

The examples below are general in nature and do not depict any specific sensor type.

Optimal Orientation of Target to Sensor

Orientation by a wall

Orientation for a turning object

Orientation for a height difference

Orientation for a turning object

Orientation for highly reflective target