`sshfs` is using `sftp` under the hood and the `umask` for creation new files is handled by the remote `sftp-server`. You can set `umask` as an argument to the `sftp-server` in `/etc/ssh/sshd_config` on the server, such as

 Subsystem sftp /usr/lib/openssh/sftp-server -u 027 # Debian/Ubuntu
or

 Subsystem sftp /usr/libexec/openssh/sftp-server -u 027 # RHEL/Fedora

The umask settings and extended ACL are not transferred through the SFTP protocol as implemented by openssh. Also note that there is no "`umask` on files", but `umask` is always associated with running process creating the files.