If you have both 32- and 64-bit Softimage installed, both versions will use the same User location. If you want separate User locations, you could modify the XSI.bat file that launches Softimage.

For example, setenv.bat defines an XSI_CPU environment variable, so you can check that and then reset XSI_USERHOME:

@echo off
call "C:\Program Files (x86)\Autodesk\Softimage 2012.SAP\Application\bin\setenv.bat"
if "%XSI_CPU%"=="nt-x86-32" set XSI_USERHOME=%XSI_USERHOME% (x86)
start "" "C:\Program Files (x86)\Autodesk\Softimage 2012.SAP\Application\bin\XSI.exe" %*

This will give you a User location like
C:\Users\blairs\Autodesk\Softimage_2012_Subscription_Advantage_Pack (x86)