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You haven't proved what you think you've proved.
No one said inquiries stopped mattering between 6 months and 1 year, they still matter, just less so. Inquiries overall are not very important to your score. Therefore the entire damage inquires will do to your score may already be capped by having 5 inquiries between 6 and 12 months old. A new inquiry doens't do any more damage, so it also doesn't do less damage when it ages off. If you didn't have any of those old inquiries, then hitting 6 and 9 months on the newer ones would be more interesting.
After 11-16, when you're down to 3 inquiries affecting your score, that will probably be more informative. And then more so at 11-21, and then you'll get another datapoint at 1-16.