I've often wondered this, but why isn't there a "medium" option for reveal?
Two things would be nice:
Firstly, a new 75% "MEDIUM" size would be nice. The sizes jump from 30% (tiny), 50% (small), 90% (large) to full width. A 70% or 75% option would be awesome.
Secondly, the size of the reveal could be screen sized based. If the user is on a medium sized screen, then the new medium or large resize could be used; if on a large screen, then the medium or small could be used.
I feel there needs to be a screen based version and not just a percentage. Similar to other settings: class="medium-resize-large reveal" (medium screen device resize to a large dialog box) or class="large-resize-small reveal" (large screen device resize to a small dialog box).
I often find the box can either look to small on bigger screens, but shrink too much on medium sized screens when using the small box.
Just a thought. ;-)