MBA mid-2012 Display Port Support

I have a Mid-2012 MBA 13", with the maximum configuration 8 gb + 512, running OS X 10.10.3. I see that this CPU will not support 4K resolution but it is supposed to support WQHD at 2560 x 1440 using a Display Port monitor. I have bought three different thunderbolt-Display Port adapters and all of them support 1080p (and audio) on two different (HP and ASUS) monitors but while the preference panel shows the resolution 2560x1440 (under "scaled") and tries to use it as "default" the whole screen gets packed into the left ~20% of the screen. I switched all of the options on the monitor, including DP 1.1 vs. 1.2, and "pixel for pixel" (which shows the 1080p in the center of the screen).

What makes this more frustrating is I plugged in my old 11" 2011 MBA, and with the same cables etc. it is perfect, gorgeous, flawless at 2560 x 1440.

I plugged into a Thunderbolt monitor at a store and of course it works perfectly. Does this MBA not support WQHD using a Display Port cable? I know it won't work with HDMI either, I get the same 1080p but no options.

I upgraded to the 2012 model because the 2011 ran out of hard drive space and had recurring battery issues. I have several work locations and I need a solution that works without investing in several $1,000 monitors.