While it may seem simple set the property set the height, it's not. There are several things to take into account:

* increased height implies bigger input. How much bigger? There is padding to take into consideration
* increased height implies scaled appearance; how do we scale?

It's not like we can't do it, but we can do so only with Javascript, which will overwrite some styles which will in turn make customization of the combobox almost impossible. So we revert back to styling.

With classic rendering (RenderMode="Classic") this would require you to create a new skin, because the entire decoration (appearance) is based on fixed size images.

With light-weight rendering (RenderMode="Lightweight") it would require a bit of tweaking, but is much easier.

With 2014 Q2, this task will be much more easier when we add elastic capabilities to RadComboBox e.g. change the font-size you change the height.

All that said, for the time being, we will not have the Height property set the height of the combobox, but rather rely on elastic capabilities in Lightweight rendering.