AWS Transfer for SFTP (AWS SFTP) customers can now create logical directory structures mapped to Amazon Simple Storage Service (Amazon S3) bucket paths. This feature enables customers to easily lock down SFTP users’ access to designated folders (commonly referred to as ‘chroot’), and simplifies complex folder structures for data distribution through SFTP without replicating files across multiple users. Amazon S3 bucket names and paths can now be hidden from AWS SFTP users, providing an additional level of privacy to meet security requirements. 

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/09/aws-transfer-for-sftp-now-supports-logical-directories-for-amazon-s3/