I change INSTALLDIR with VBScript, but file location isn't changed

[anatoly_medynts]

Install Shield LE
I changed INSTALLDIR property with VBScript (After Initialization custom action), during installation installer shows that target directory is new, but file location after installation isn't changed. How resolve this problem?
Remarks: If I press Change button on the Destination Dialog (that shows changed value) just close SelectDirectory dialog without any change in the changed path - all works correctly

[anatoly_medynts]

I found correct variant:

Session.TargetPath("INSTALLDIR")=

It works