Ah! I actually shifted the paddle a little higher very late in development. I hadn't tried it on mobile until I uploaded the HTML5 build to itch, and when I did I discovered that having the paddle right at the bottom of the screen meant my finger obscured it while trying to use touch controls. It probably is a little close rather than a little far at this point: in hindsight a check to see if the player is on mobile (and a shift in paddle position if they are) might have offered the best of both worlds.
When it comes to the sideways-shooting dice, I've got no idea what's doing it. If I were to remake this I'd probably specify movement rules rather than simply rely on GDevelop's physics engine for everything, though I am rather fond of the exploding dice myself!