Helix Syn not long enough?

So tonight I gave a go at my helix syn with little to no success. trying for at least 30 minutes with slightly different variations of breathing, positions and muscle movement. My girlfriend gave me her womanizer duo to try instead. I managed to hit the spot perfectly with it and had an orgasm. I clamped the length of the dildo portion and compared it to the aneros. I found that the aneros is about half an inch short of hitting the spot. Is my prostate just deeper in or is the movement just too delicate and requires more hardwiring?