This is my code to set the label on the bottom of the button Icon.
m_button.setIcon(large);
m_button.setLabel(m_button.getName());
m_button.setVerticalTextPosition(m_button.BOTTOM);
m_button.setMargin(BUTTON_INSETS);
m_button.setSize(BUTTON_SIZE);
m_button.setSize(20, 20);
But the result is the below one.