The scale of the buttons is calculated based on the screen density as reported by the device. I have tested this calculation on several devices running both Android and iOS, including several iPhone and iPad versions to make sure the buttons are the correct sizes for any screen. However, sometimes the dpi value is not accurate and it's possible that on some devices the buttons are too large or too small for the screen. You are the first to mention this issue, and I am looking into fixing it, but it may take some time because I am also already in the process of adding some new features to the game which are not quite done yet. I do hope to have a new version out soon, so please be patient. Thanks for your feedback and your interest in the game.
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There is an option to hide the controls.
1. Tap the gear button at the top of the screen
2. Choose "Game Settings..."
3. Set "Touch Controls" to "HIDE"
Now the controls will be hidden so you can see the whole screen, but they work the same as before and they light up only when you touch them. Give it a try!