Here, I mounted this very spade onto a banana plug adapter. You can clearly see that in addition to the spade blades. The round nut and curved portion of the spade do indeed make contact. Torque it down and you have a superb connection! I could have soldered the solid core wire curved off to one side and that would have made more surface area available.
http://s301.photobucket.com/albums/nn76/reb1208/?action=tageditmany
http://s301.photobucket.com/albums/nn76/reb1208/?action=tageditmany