You need to extend the lowest (largest diameter) portion of the antenna fully when the transmitter is on. I believe a range check of at least 50 yards with the antenna partially extended would suffice. Of course, you'd want to extend the antenna all the way for any flight.

Do you have a non-synthesized module that matches the frequency of your plane? If so, install it, collapse the antenna and range check it until you DO get a glitch. Then install the synthesized module, partially extend the antenna and perform the range check again, until that setup glitches at the plane. Now you'll have the definitive answer, and you can tell the rest of us. I don't have a non-synthesized module for my 9CAPS, or I'd do it myself. (No, I'm not a Futaba Rep.)