I'm not sure if I entirely understand. Are you trying to keep an enemy from being placed randomly on the map before the game loads?
I never really but mobile controls into thought, if I'm honest.
But OH MY GOD that is a genius idea, and your idea will be taken into consideration for an update and future games.
In the menu, you can use the down arrow to change your selection, and space to select.
The how to play section will tell you how to use your controls ingame
This is an insanely well made game, especially the graphics! Nice job on making something so impressive. May I ask, where or what do you use for your graphics?