Access Logging's early upload does not start when Global Limit is set to 0 mbyte
An early threshold upload should happen at the specified value. If you want an upload to start at 1MB then it should be specified.
It is very important to understand Early Threshold settings. The global early threshold is the sum total size of all of the logs. That is, if the sizes of all of the logs equals the global early threshold then the most recently written log facility will get uploaded.
It is best to set the per facility early threshold if you want that log facility to upload at a specific size threshold.