E-Dock Plus Display Resolution Issue

I have Dell E5540, Dell E-Dock Plus, Dell U2412M, Dell S2240T.  The U2412M is using DVI-D and S2240T is using VGA.  Windows 8.

I can only get U2412 (primary display) to 1920x1080 not 1920x1200.  Can someone help explain to me how to get to 1920x1200 on U2412 please?