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PPK result for more challenging situation highly depends on the algorithms the post-processing software uses.
A customer that didn't have good PPK result using RTKPOST suggested below online PPK site that produced good result.
https://kernelsat.com/topaz/topaz_about.php
Reason for the performance difference likely due to the TOPAZ software already included optional tweaks that user of RTKPOST may need to manually select, such as forward/backward combined processing, using more advanced Iono/Tropo correction model,...etc. which may not be obvious to a first time user.