Not really bro. It goes by a certain threshold value. Once the signal is not strong enough, it will be conservative and revert to 2G. Depending how weak is the signal, forcing the phone to use 3G band may work. But it is not recommended because weak signal will cause your phone to consume more battery.

I do not have a Zenfone. I'm one of those early Android adopters (think Android 1.5 ) and we used to set it via hidden testing menu. I am not sure if this is still valid to Android phones nowadays. But I did test it on a cheap Alcatel running Android 4.0, it still works. Here are the steps:

Call *#*#4636*#*#
It will bring up the hidden Android Testing menu. Go to Phone information. You will see a drop down list of "set preferred network type". Select WCDMA only. This will force your phone to run on 3G band. However, take note that if you are in a location with strictly 2G coverage only, you will get 0 signal.

Strava kaki ??
GPS ok? Elevation data accurate? Lol