During Installation, the value obtained from the user is used directly as the installation path. For example if the user enters "c:\program files", then your program will be installed to "c:\program files".
If you want to force a subdirectory to be appened to the path selected by the user, you can do this by changing the " Installed EXE name" field. For example:
User selected Install Path = c:\program files\mydir
Installed EXE name = %ProgramName%
Resulting %InstallPath% = c:\program files\mydir (installation EXE package filename is used for main EXE name)
Installed EXE name = forced_sub_dir\%ProgramName%
Resulting %InstallPath% = c:\program files\mydir\ forced_sub_dir Installed EXE name = ..\ forced_sub_dir\%ProgramName% (.. causes the installation path to be placed one directory back from user selection)
Resulting %InstallPath% = c:\program files\ forced_sub_dir Installed EXE name = forced_sub_dir\ forced_exe_name.exe
Resulting %InstallPath% = c:\program files\mydir\ forced_sub_dir(main EXE is called forced_exe_name.exerather than using the installation package EXE filename)