The dash is designed to open "half-way" for screens that are larger than a standard netbook. This is called "Desktop" mode.

You can force it to use "netbook" mode through the following:

gsettings set com.canonical.Unity form-factor 'Netbook'

If you want to reverse this try

gsettings set com.canonical.Unity form-factor 'Automatic'

or

gsettings set com.canonical.Unity form-factor 'Desktop'

Alternatively, you can install the configuration editor dconf-editor from the package dconf-tools and do the same the graphical way:

for 12.04

For 12.04 and later you can use MyUnity:

There is also a rather neat overlooked method...

Click the dash maximise button as shown, followed by the dash button itself. This changes from desktop to netbook and most importantly the setting is retained when you logout and login.

For other options:

• How can I configure Unity?
• How to get the Unity dash overlayed not maximized by default?

One (somewhat hackish) solution could be to simulate a Super keystroke every time you log in.

You can do this by adding the following xdotool command to your Startup Applications:

xdotool key Super_L