New log system with filters may be worth a look. There are more options in latest canary than in 2.0.3.3 beta. I’m somewhat confused by the question. For controlling sending, use --send-http-level, to set outcomes which send logs. The --send-http-log-level is seemingly like similar controls on other logging, and sets the threshold to control line-by-line what goes into the log, which the --send-http-level setting may or may not actually send.
As for command line versus GUI, I think these are the same. In GUI, you set advanced options, and read help:
send-http-level You can specify one of "Success", "Warning", "Error", "Fatal". You can supply multiple options with a comma separator, e.g. "Success,Warning". The special value "All" is a shorthand for "Success,Warning,Error,Fatal" and will cause all backup operations to send a message. Default value: "all"
send-http-log-level Use this option to set the log level for messages to include in the report Default value: "Warning"