@calmh, I think you told me once that before a transfer some index data is exchanged so it might look like Syncthing is not doing anything.
I only notice this on large files, eg. 25GB, that after scan there is a long pause where only a couple of KB/MB is exchanged in the first 5 or more minutes (note: I have a medium range device with spinning hdd, so this might also amplify this). Once this is done uploaded speed is maxed out as expected.