'Select Similar' doesnt'add to selection

I've got mine set to shift-F (no connection) and ctrl-shift F, and it only works on the highlighted geometry as long as nothing is selected. As soon as something's selected, it only works when I select a face on the part I want to select first and then press the hotkey again.

edit: it would also be nice if this could use the scrollwheel to set the sensitivity interactively as long as the hotkey is held.

Which tool are you talking about, "Select Similar" or "Select Similar Facing"?