I would like to share my experience with you. I have received data on ttnmapper from 120km away. Since it is an indoor gateway, and is located in a small depression, this is very far. So I looked at https://www.heywhatsthat.com (line of sight calculator). Exactly from where I received data it shows a line of sight, so the data seems to fit together very well.
According to heywhatsthat.com this is the largest possible line of sight.