There's no point making shotgun changes without understanding what's happening. Can you test some other export options and see if they're the same? That will determine if it's a C2 or Cocoon issue. It might be worth checking the window inner width and inner height sizes in each case too, since that's the most important determinant of the game canvas size, and if it's even 1px smaller it might push letterbox integer scale down a level. So for example if Cocoon's window inner size was just 1px off, it'd have this effect. And that'd be a Cocoon issue, not a C2 issue, and not something you want to go tinkering with JS to work around.