Don, you are obviously much better versed in the theory of harmony than I am, but I have to take issue with your contention that it only takes three notes to make a diminished chord, no matter what the theory might say.

When B,D, and F are sounded together whether simultaneously or as an arpeggio, the western ear will automatically hear a G7 chord,( subconsciously interpolating a G) and want to hear a resolution to C major. The fact that the three notes together are called a dimiminished triad by theorists is neither here nor there. However , if you add a G# then the listener's expectation is totally changed, and you do in fact have a diminished chord.

Murray