Not exactly what you'd asked for, but as close as I could get it, and certainly smaller than any other tracking window I've ever used.
Features:
- Con checkboxes, Track button, Close button, and Filter dropdown autohide when the mouse isn't over the tracking window
- Minimum height and width set to exactly match the minimum space needed by the window contents
- Vertically-arrayed Con checkboxes
- Smaller Track and Close buttons (renamed from OK and Cancel)
- Smaller list font (Arial14 instead of Zapf15)
See attached screenshots for examples of the window in action at minimum and larger sizes with the mouse hovering over the window and without it. (Screenshots taken with frame and backdrop set to 0% normal, 100% mouseover)