Hi,
Try changing the minimum word length full-text parameter, e.g. innodb_ft_min_token_size for InnoDB on MySQL search indexes, witch is 3 by default.
Modify the parameter valid for your db and engine, restart the service and re-index de table with an appropiate command like ‘OPTIMIZE TABLE rt4.AttachmentsIndex;’ in my case. It may take long (hours) but once finished, you can try searching with “+11 +22 +33 +44 +aa +bb”. Non alphanumeric characters are ignored.
I’ve tried with innodb_ft_min_token_size=2 and it works nicely. Take a look at https://dev.mysql.com/doc/refman/5.7/en/fulltext-boolean.html for more info.
Hope that helps.