The Evo One Speaker Placement settings are designed to adjust for the distance between the back of your Evo One and the nearest wall.
A speaker's proximity to a wall can influence its sound. When placed too close, for example, reflected sound waves may result in an unwanted emphasis on certain frequencies.
You can adjust the Room Compensation settings in the StreamMagic app by selecting 'Room Settings' in the app home page, and then 'Speaker Placement', which will take you to the section below. Once you've enabled 'Speaker Placement', you can then move the slider to approximate how close the back of your Evo One is to the nearest wall.