Most of apps, that I am using on my Android phone does not take into account fact, that red areas exist.
How people hold and interact with mobile phones:
Two methods of holding a touchscreen phone with one hand:
The two methods of cradling a mobile phone:
Two-handed use when holding a phone vertically or horizontally:
Surely there is more interesting and useful information in the article, so I advice to read it as well, not only to look pictures.