How do you setup tab settings for user defined file types in notepad++?

I'm trying to setup Notepad++ to be able to edit a particular source-code file (*.mrc / mIRC Scripting File). The only thing I can't figure out is how to set the tab settings to 3 spaces.

I've searched google, however, I can't seem to find how to do this. The extent of what I search brings me to the setup for a user-defined language which I've already pretty much done. Tabs are the last steps.

When I add my user-defined file type to notepad++, the extension doesn't register in the Settings > Preferences > Language Menus tab. >:/