As a user experience designer, I pay very careful attention to the needs of mobile users. Today's mobile devices are getting larger screens and with that, the context of how users engage with their devices is changing. When is the last time we studied how users actually hold their phones? According to a 2013 study by Stephen Hoober, there are three ways that users hold their phones:
One handed - 49%
Cradling - 36%
Two handed - 15%
I'm sure these numbers would be quite different today given the number of phones with larger screens. Of course we change positions often while using our phone based on the UI of the app or because of real-world factors like subway stops or stoplights. Does this mean we should be avoiding the dreaded upper-left corner because most users are one handed and right handed? It definitely makes the problem more complex. I think we should realize that the user is flexible, but perhaps we should design our UI to reflect the position we would prefer our user to take.