Can the signal level at which Wi-Fi disconnects be changed? On my iPhone 5s, I am often at a location at the edge of the limits of my Wi-Fi  signal, where my 4G signal will actually be stronger than the Wi-Fi  signal. However, my iPhone will remain connected to the Wi-Fi  at this point, and will only disconnect when there is no Wi-Fi  signal at all.

Is it possible to increase the level at which Wi-Fi  will disconnect and the 4G (or 3G) will be used instead? As it is, I have to manually turn off Wi-Fi  every time this happens, which is rather frustrating.
Not configurable on iOS.  

Depending on your Wireless Access Point/Router you can sometimes turn down the signal power to shorten it's reach to a smaller radius.