Gigapixel PNG Export Issue

Hi I am trying out the trial version of Gigapixel 6.2.2 and when exporting as PNG, no matter what output compression - 1 to 10 - settings I use (or just preserving the source format), it does not seem to make any difference as the resulting file is always the same Mb size and the processing speed when saving is also the same no matter the output settings chosen. Am presuming a 10 compression should give a smaller file size than a 1, but is not the case. Please let me know if I am missing anything here.