Here is a list of all the WPR-15 stations who have heard my beacon signal within the last few days.   The maximum distance of 1900km is about the same as the WSPR-2 transmissions made earlier this year at the same EIRP.  I'm guessing there are a several reasons here:

1)  These summer months give reduced S/N / propagation and offset the theoretical 9dB gain

2) There is a gap in plentiful station locations from those around 2000km (Eastern and Northern Europe) to the next group of US ones at 5000km +

3)  WSPR-15 does not have 9dB advantage on longer paths due to propagation artefacts.  Perhaps fading and breaking it up.

Anyway :

Andy  G4JNT