Aneros makes me ejaculate; Am I doing something wrong?

Apologies, this got a little longer than I anticipated.

First, a little background info. I've been using my Helix Syn for about two years, quite infrequently since I don't get a huge amount of time to myself. I tend to use it once a week, though there have been longer gaps between my sessions. I'll usually masturbate with my partner once between aneros sessions (I haven't introduced him to the aneros, since he's a little bit funny about sex toys).

It took a while before I started to feel any kind of good sensations down there, but they began to happen a few months ago. I think I finally learned to relax into the sensations. Before, I'd get overexcited at the slightest feeling and tense up. I've had some good sensations from the Helix, and I always look forward to my next session to see what else it can bring, though I usually finish with a TO.

I haven't experienced anything particularly orgasmic except on two occasions, which this post is about. Very recently (in the last month), I've had two instances where the aneros has made me ejaculate with no penile stimulation. When it happens, I feel the Helix pushing up really hard inside me, pressing hard against my prostate as though squeezing the cum out. It feels good, really good, but afterwards, my sexual energy vanishes and it's basically the end of the session. I'm fairly happy with this, since I feel like I'm finally getting interesting results from prostate play. However, I've yet to experience a dry orgasm, or multiple orgasms.

During my sessions, my penis is always rock hard. It's always been the way that I can get hard very easily. Even just thinking about something sexual will make me hard. I wonder if this is holding me back from true prostate orgasms, like my erection is redirecting that sexual energy to my penis rather than to my prostate / other parts of my body. It's unfortunate, because now when I feel the ejaculation start to build up, I'll back away hoping to prolong the session. Then I'm no longer relaxed and struggle to get any sensation from my prostate again, which is counter-productive.

Is there anybody else out there who has had similar experiences of hands-free ejaculation from the aneros followed by loss of arousal? Am I on the right road to experience MMOs, or even Super-Os? Is there anything I can do to progress past hands-free ejaculation into dry orgasm? Or is it just a case of continuing to experiment?