Upload Speed reduced with MocA but not Download.

With an online speed test, I have 600 Mbps download and 900 Mbps upload when connected directly with ethernet. Once I set up the MoCa connection I get 600 Mbps download but only 450-500 Mbps upload. Is there any reason why the upload speed would drop while download stayed the same? Can this be adjusted by changing any of the settings? Thank you,