I just called Airbnb on this, you're finding out the hard way like I am. Its not simply your response, it also calculates if you decline inquiries and/or cancel reservation requests. In my situation I responded 100% within minutes, however I declined multiple inquiries for people who wanted to stay longer than my limit. Ive been told 2 ways to combat this I need to change my setting from "Manually review and approve requests" to "dont allow reservation requests. I have also read to not decline it, but ask them to recall the inquiry/reservation
There is no need to ever decline an Inquiry- just messaging back within 24 hours is enough to keep up your response rate. So not necessary to ask the guest to withdraw it.
Requests you do have to ether accept or decline within 24 hours, so if it's inappropriate, and you can get the guest to withdraw it within that 24 hours, that saves you from having to decline it.