Resolution not correct on MBA external display

Hello,

I have a mid-2011 11' MBA running 10.7.3. I recently bought 3rd party mini displayport to hdmi converter to connect my mba to lcd screen but it seems that the resolution of the external display is always misjudged by the mba. I can set the external display resolution from as low as 1024 x 768 to (desired) 1080p and resolution looks ok, quality is fine. But the problem is the display slightly extends over the top and bottom of the external screen. It is not much but I can only see the bottom half top bar and also part of the dock is missing at the bottom. The situation persists even if I use the mba and external display side to side or use only external display. The resolution on the mba display is always correct, it always fits to the internal monitor. This is so frustrating as I watch most of the movies in very high quality and don't want to miss parts of them. The same LCD screen is working ok with laptop pcs and wd live tv at 1080p and other resolutions. Is there any fix to this problem, your help will be much appreciated.

I am sharing sample screens to explain my situation better. This is the MBA's screen and what should be replicated in external display: Internal mba display | Flickr - Photo Sharing!
And this is what is displayed on the external, notice it is cropped on top and bottom:
external display | Flickr - Photo Sharing!

In order to get the correct resolution and aspect ratio on the external monitor, you have to run your MBA in "clamshell" mode. Otherwise the external LCD will default to mirror the MBA. See the following Apple KB article for instructions:

LINK

Frankly I don't see how running the MBA in clamshell mode will help in my situation. But while playing with the settings I saw there is a setting named underscan in system preferences -> displays where you can set the zoom level of the external display. So if the aspect ratio is correct you can fit the screen manually with playing with this underscan parameter. May it help to other mba users who encounters the same problem.

Instead of negating what I replied, why don't you try it and see? You can do all the over scanning and under scanning that you want, but you will not achieve the correct resolution on that external LCD with the lid of the MBA open. At least not without distortion. But that's up to you. It's your eyes.