Actually, I'd like that change on larger devices as well. I've often misvoted on my Surface. As large touchscreens become more popular (iPad Pro, the Surface line, etc), I could see this becoming a problem for more users.
Edit: I see white margins on my iPhone 5, but not on my iPhone 6. It looks like you need to tweak the media query in the following css:
@media only screen
and (min-device-width : 375px)
and (max-device-width : 667px) {
...
The iPhone 5's device width is 320px. Changing that 375 to something lower should fix the issue.