I don't think you can use that format above because I've checked the official help (available online) and it appears that the @ symbol doesn't appear to be used instead you define the domain, username and password and then use the Tab function to switch between login form elements to type the address.
Since the WinKeySim is pretty old, I recommend checking AutoHotKey. It's better and has support for all the keyboard items: https://autohotkey.com/