HIH 950 vs Other aneros models

Alright so I'm looking at the HIH 950 and have heard some good things about it.  For the few who don't know, High Island Health also owns the aneros brand.  Here is what I'm curious about.

The 950 is said to give a thorough prostate massage.  However it's a good deal smaller than the aneros models.  For example the Helix is quite a bit bigger.  Both models claim to give a thorough prostate massage but I'm confused as how the Helix for example can claim this when it's longer.  If a person has a huge prostate I could see this but even though the helix does move pretty well, I don't see how it could hit the prostate if the 950 is able to give a good massage.

I'm just wondering if someone could explain this to me?  I could be completely wrong but just don't see how these models can offer the same thing as the 950 when there is such a difference in size.