I get it now. Thanks for your terrific explanation.

This isn't incredibly important but I do have one more question: why can't I seem to get the size of the drop down as small as an icon? The size property isn't adjustable in the properties window except by changing the font size - which is strange considering I have chosen Image Only as style.

I changed the drop down to Image and Text and added a description of the icon, which actually looks great, but I'm still curious as what's going on.