Existe uma configuração no arquivo vsftpd.conf:
file_open_mode
The permissions with which uploaded files are created. Umasks are applied on top of this value. You may wish to change to 0777 if you want uploaded files to be executable.
Default: 0666
Simplesmente mude o modo para 0777, então com o umask adicionado você recebe 0700
Ref: link