Interestingly, both LA3ZA and SI9AM are using just 200mW on 10m yet they are both coming through fine here on 10m WSPR. SI9AM is a few dB stronger than LA3ZA, which I assume is propagation. I use 2W as my Par end-fed antenna seems to be somewhat of a compromise. I don't want to take it down as it get me on several other bands too.
UPDATE 1200z: Still waiting for that elusive F2 propagation. The ZS is not currently listed in the 23 active stations.