Files installed to C:\ instead of C:\folder\ - nsis

Question

My installer copies Uninstall.exe and /temp/ directory to the installation folder (for me it is C:\MyExample), but MyExample.dll/ico/exe, and success/error.wav are copied directly to C:\ and I can't get this working.
!include "MUI2.nsh"
;General
Function .onInit
ReadEnvStr $R0 SYSTEMDRIVE
StrCpy $INSTDIR `$R0\MyExample\`
FunctionEnd
Name "MyExample"
OutFile "Setup.exe"
RequestExecutionLevel admin
;--------------------------------
!define MUI_ABORTWARNING
!define MUI_FINISHPAGE_RUN
!define MUI_FINISHPAGE_RUN_FUNCTION "LaunchLink"
!define MUI_FINISHPAGE_SHOWREADME ""
!define MUI_FINISHPAGE_SHOWREADME_NOTCHECKED
!define MUI_FINISHPAGE_SHOWREADME_TEXT "Create Desktop Shortcut"
!define MUI_FINISHPAGE_SHOWREADME_FUNCTION finishpageaction
;--------------------------------
;Pages
!insertmacro MUI_PAGE_WELCOME
!insertmacro MUI_PAGE_LICENSE "${NSISDIR}\Docs\Modern UI\License.txt"
!insertmacro MUI_PAGE_DIRECTORY
!insertmacro MUI_PAGE_INSTFILES
!insertmacro MUI_PAGE_FINISH
!insertmacro MUI_UNPAGE_WELCOME
!insertmacro MUI_UNPAGE_CONFIRM
!insertmacro MUI_UNPAGE_INSTFILES
!insertmacro MUI_UNPAGE_FINISH
;--------------------------------
;Languages
!insertmacro MUI_LANGUAGE "English"
;--------------------------------
;Installer Sections
Section "Dummy Section" SecDummy
File "MyExample.exe"
File "MyExample.ico"
File "error.wav"
File "success.wav"
File "MyExample.dll"
CreateDirectory $INSTDIR\temp
SetOutPath "$INSTDIR"
WriteRegStr HKCU "Software\MyExample" "" $INSTDIR
;Create uninstaller
WriteUninstaller "$INSTDIR\Uninstall.exe"
WriteRegStr HKLM "Software\Microsoft\Windows\CurrentVersion\Uninstall\Product\MyExample" \
"MyExample" "$\"$INSTDIR\uninstall.exe$\""
SectionEnd
Section "Uninstall"
# Always delete uninstaller first
delete $INSTDIR\uninstall.exe
delete $INSTDIR\MyExample.exe
delete $INSTDIR\MyExample.ico
delete $INSTDIR\error.wav
delete $INSTDIR\success.wav
delete $INSTDIR\MyExample.dll
SectionEnd
;--------------------------------
;Descriptions
LangString DESC_SecDummy ${LANG_ENGLISH} "Setup"
!insertmacro MUI_FUNCTION_DESCRIPTION_BEGIN
!insertmacro MUI_DESCRIPTION_TEXT ${SecDummy} $(DESC_SecDummy)
!insertmacro MUI_FUNCTION_DESCRIPTION_END
;--------------------------------
;Uninstaller Section
Section "Uninstall"
Delete "$INSTDIR\Uninstall.exe"
RMDir "$INSTDIR"
DeleteRegKey /ifempty HKCU "Software\MyExample"
SectionEnd
Function LaunchLink
ExecShell "" "$INSTDIR\MyExample.exe"
FunctionEnd
Function finishpageaction
CreateShortcut "$desktop\MyExample.lnk" "$instdir\MyExample.exe"
WriteRegStr HKEY_CURRENT_USER "Software\Microsoft\Windows\CurrentVersion\Run" \
"MyExample.exe" "$INSTDIR\MyExample.exe"
FunctionEnd

Answer 1

In your Dummy Section section, you are installing some files without telling the destination directory. I suppose that implicitly meant $INSTDIR, but you need to be explicit as a section might or might not be selected (when you have multiple sections), and they must not rely on side effects of previously executed sections (if ever).
Add the destination folder at the beginning of the section, before the File statements:
SetOutPath $INSTDIR