I've read through What are the best techniques to play overtones in the saxophone? but I can't seem to move forward. I've gotten to the point where I can play the first harmonic, as in an octave above, but for lower notes such as C and below, I always produce a fifth above the octave, the second harmonic, never reaching the first harmonic.
But my real struggle is playing a fifth such as an A with the fingering for D. I've used the trick where I first finger A then go to D, and I can sustain A that way, but I'm never able to play A with D fingering without switching. Is there any technique other than just playing over and over again? Is there something I'm missing?