Audacity Problem - Volume Peaking at 0.5

How can I prevent a half-volume mono recording?

This can occur when connecting to one channel only of a device that has separate left and right channel inputs. Recording in mono will often result in a half-volume track that cannot be made louder without adding distortion. If this happens, record in stereo using Device Toolbar, then use the Audio Track Dropdown Menu to split the stereo track and close the silent channel.
(Link)