it doesn't give a clean settings sheet like I'm used to
Because mIRC is always reading your settings from the directory listed above. The only ways to get mIRC to use another mirc.ini are to do ONE of the following:
1) Run mirc.exe with -r or -portable to tell it to use the current directory for mirc.ini. You can setup a shortcut to pass these parameters to mIRC when launching the program. See /help Command Line for more info on this.
OR
2) Copy mirc.ini into
the same directory as your mirc.exe. mIRC will automatically use this file instead of your AppData directory.
NOTE:
DO NOT do either steps if your .exe file is inside of Program Files\. Weird things will happen if you attempt to do this. If you want to run with different settings files, move the exe out of Program Files and into another directory.