Tonight I gave Flappadiddle a quick test on iOS.
I've expanded the "ground" on either side, making them slightly taller and wider.
This is where your thumbs will go whilst playing the game.
Unfortunately, they're still a little "too" close to the bottom of the screen, and weird "iOS Slider" glitches are occurring.
You can see at about 35 seconds into the video, I accidentally trigger the bottom slidery thing to pop up briefly.
This is frustrating.
Also, as about 1:30 you'll see me oddly flap straight up, as the controller glitched out a second time, and didn't register me holding left.

Really annoying!!

Hopefully I can fix these issues, most likely by expanding the "ground" up, a little bit further, although I'm also well aware that I'd need to avoid getting to the point where you're filling 90% of the screen with your giant thumbs!!!

But.. It's workable, I think.
I'll be doing a few more tests over the next few days, and will let you know how it goes.