I’d say a better evaluation of the effectiveness of the I90 Spheres is Phonak’s “Scientific Poster.” The tested users were all fit with couplings with only a 1 mm vent. At the very least, the survey could have broken down responses according to the type of coupling (mold or dome). So, from my own experience with power domes, I’d say the survey results imply to me that a large number of respondents probably had a much more open fit and weren’t getting the noise reduction possible with a more closed fit. Several Sphere purchasers have mentioned on the forum that they wear an open fit. So, it’s unsurprising that some respondents are not getting the maximum Spheric Speech Clarity effects. I would say that’s the best one can likely conclude from the forum survey results as compared to the carefully controlled experimental results in Phonak’s Scientfic Poster: Phonak Sphere Infino - experience with open domes - #2 by jim_lewis
The best compromise for combining Spheric processing with an open fit would be to get Phonak’s ActiVent receivers, which close the venting in very noisy situations or for streaming and are otherwise open. But this is an expensive, high-maintenance solution. I’d rather just wear a closed fit as I always have to get the best noise reduction and directional speech when needed from my HAs.