Royal Mail not delivering my mail even though I saw him outside my house. Anyone have any idea what’s happening?

Let me explain my thinking. When I'm in for a parcel, people knock on my door and hand me the parcel when I answer it. When people leave a parcel, it's because I wasn't in. So, in my world at least, parcels routinely being left would be indicative that the people who deliver parcels were not getting a response when they knocked on the door. However, I do lived in a terraced house. I'm conscious that drivers will leave parcels without waiting for an answer at the door, or even ring the bell sometimes, when it's safer to do so. I didn't know at the time that you had such an arrangement. I presume you do. It's not an unfair assumption for me to assume that people would knock on your door to deliver parcels, even if it is incorrect. I rest my case. 10 doors down, because it doesn't look like you're in, tbh.