What is the "loop around the back" trick on Sky Force Reloaded?

A couple of people have said that they've used the "loop around the back" trick on Sky Force Reloaded, in order to defeat the Boss. How is this performed?


When fighting with some bosses, there will be no place to run on bottom of the screen. Then you can loop around the boss since there won't be any gun fire behind the boss. The level 13 is good example for this.