CRM 2013 new form layouts prefers 3 column tabs with 1 column sections over the CRM 2011 1 column tab with 2 column sections. The nice thing about this new layout is that as you resize the browsers window the containing sections will arrange themselves to fit cleanly within the window. This is typical behaviour of floating elements. So for example as you shrink the size of a window a tab with 3 horizontal sections will start to stack on each other vertically. While creating a few custom entities I noticed a slight rendering problem when resizing the CRM’s window. The gap between the final field is a section and the next tab would increase. Take a look at the screen shots below.