I mentioned last time that I love Overlays on the UI. It is another way for the architects and designers to add another, ahem, layer of interactive functionality to data-rich web application screens. And in the financial industry, there’s still this prevailing idea that the more information presented to the end-user, the better that individual’s decision-making ability. That is utterly false. Information should be compartmentalized and organized to inform in the most intuitive manner possible.
Most of the applications that I deliver are web applications that target the desktop screen sizes. These applications are used at work offices primarily, and rarely do they have a requirement to be used on a mobile phone. The closest thing to a portable device has been a tablet, but even those have a decent resolution.
To the point, UI Overlays should not be used in mobile phone screens. So despite all my rave, they have no place in screens smaller than 768 pixels. You simply do not have enough real-estate for yet another popover to show up on a small screen. Not to mention the amount of frustration that users will feel when they have so many buttons on the screen clamoring for attention. If you must, consider collapsible panels instead.