I’ve noticed while using ACF that fields don’t go full width while using a 2560×1600 resolution. I then decided to type 100 into the width % field to try to force the desired behavior but upon noticing that had no effect, I realized there was a “hard coded limit” of 1400px being set upon inspection with Firebug.
So, right now I have overridden this with css and an !important directive but 100% should equal 100% rather than some arbitrary artificial pixel boundary IMO. Agree or disagree?
Using ACF v5.1.5 / WP v4.1 on PHP v5.4.x / Apache (Local)
The latest version has been improved to ensure that you can set the width of your fields.
Just update to the latest version to enjoy these features.