What you said about 7/7 folks being in the minority may be true for your own search criteria, but maybe not for Ben and certainly not for me. I did little experiment with one of my searches. Not changing any other criteria in this particular search, if I change the church teachings to "no preference", I only jump up from 74 results to 77. That's not a very big increase. There are only 3 girls out there worldwide that are being ruled out by the 7/7 filter under that particular search. But then again, I'm looking for girls who list themselves as conservative or very conservative as far as politics goes. I think that may have a large part to do with it as well. In other words, if you're looking for a conservative girl who is not 7/7... then you're probably going to have a hard time. And I have noticed that with some common interests (such as "Lord of the Rings" under one of my searches) conservatives or 7/7 girls tend to make up the majority.
So again... it depends on what you're searching for. I assume a search with an emphasis on liberal politics might have 7/7 girls in the minority.
Perhaps someone else will do their own experiments and post the results.
Without access to the entire database, it is hard to know the reality. Perhaps we are like the story of the blind men describing the elephant, each of us sees the same database very differently, through our own filters.
I would note that some 7/7 folks are willing to look at 6/7 or even 5/7 folks, so if you are sending out letters to 7/7 folks and are not 7/7 yourself, you could still get responses, but at a reduced rate. In general terms, I would assume that response rates would be higher if the person you approach is more like yourself, in whatever field you want to compare. I have certainly found that I am much less likely to get a response from ladies more than two years younger than I.