There are two options related to quotas:
--quota-size, which looks like it isn’t hooked up to these warnings, unfortunately
and
--quota-warning-threshold, which you can use to set the percentage threshold where a warning is given (if you set it to 0, it should disable the warnings unless the SD card fills up completely)
The quota detection attempts to get the free space at the destination path, but could be missing some logic on Linux.