Tabbed Navigation - Increase area height of drop down(Top to bottom)Child Object list to eliminate vertical scroll

In 800xA 6.0.3.2 Tabbed Navigation, if number of levels tabbed are 3 or more then child objects appear as drop down list. And if number of child objects are more, a vertical scroll bar appears. (As I have selected Top to Bottom option on TabGrouping - > Tab Appearance tab in workplace structure)

Is there any way to get rid of this vertical scroll bar..?
In other words, to increase area height of drop down(Top to bottom)Child Object list..?

Any suggestions highly appreciated.

Thanks in advance.