MS SQL transaction log backup

[Zek]

When job doing periodically MS SQL transaction log backup, it create temporary .BAK files on local partition.
1) Help centers says "To keep log files, Veeam uses the volume with the most space. Such a volume is detected automatically during the initial session of the backup job." But often I see temporary files on a partition with less free space then others, even after child "SQL server transaction log backup" job recreated, and reg key "HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Backup and Replication\SqlTempLogPath" is not changing.
When exactly guest helper should detect volume spaces? Is this determined only once, on first backup session, and storing in registry permanently?
2) Does backup job use default MS SQL server backup-compression settings for temporary .BAK files, or can I manually specify compression option for database backup to reduce space usage inside VM when transferring data to proxy? When database generate hundreds GB logs per minute, this becomes important.
Does this affect storage log compression in the repository (.vlb)? Are there any best practices backup transaction log settings to optimal storage usage in the repository?

[foggy]

1. The disk is selected once during the initial job run and then is not changed unless you modify the mentioned registry value.
2. Logs backups (VLB) are compressed depending on the job settings. I need to check regarding temporary BAK files though.

[foggy]

Temporary BAK files do use SQL native compression by default unless it is SQL Express.