backup log larger than log file
Your T-SQL BACKUP LOG command does not use the INIT option.  If you do not specify the INIT option, and the file target backup file already contains one or more backups, the backup you are taking is appended to the end of the file.

This would explain how your log backup seems larger than the log it backed up.

You can tell if there is more than one backup in the target file by looking at the results of:

RESTORE HEADERONLY 
FROM DISK =  N'g:\sqlbackup\LOG\myDB_LOG_20160329_084501.trn';


See the "Media Set Options" in the Backup MSDN page.