How to show a modal form on top of its owner form (its owner is set to fsStayOnTop or not), just as TOpenDialog does

Question

Summarization:

Please see the helpful comments below from Craig and Sertac.

======================================================

As shown in the following minimized code, TForm10 is set to be fsStayOnTop. TForm10.btnTryDlgClick call dlgOpen1.Execute, and the dialog shown is as expected. However, when I call TForm11.Create(Self).ShowModal inside TForm10.btnTryFormClick, the form is hidden behind the TForm10. I am wondering how to understand this behavior, and why standard TOpenDialog can show as expected? Any comment is appreciated!

PS: One workaround is to override the CreateParams procedure of TForm11, and set Params.wndParent to 0. But it looks to me that window hierarchy will be broke using this workaround.

  procedure TForm11.CreateParams(var Params: TCreateParams); // override;
  begin
    inherited;
    params.wndParent := 0;
  end;

PS: Another workaround is mentioned by Remy in the below relevant SO pages: setting the modal Form's PopupParent property to be the StayOnTop Form. But in the followed comments, Sertac mentioned this workaround will also break window hierarchy.

PS: Possibly relevant SO pages:
Modal forms hidden by fsStayOnTop forms
How Can I Keep the FindDialog from Staying on Top (Delphi)?
How to make sure a dialog is always front of the main window
Form is hidden behind other forms when ShowModal is called
Make 2 forms able to overlap each other?
Multiple form Delphi applications and dialogs
Newly created modal window loses focus and become inacessible in Windows Vista
Delphi - How to prevent Forms/MsgBoxes to move under prior form?
How to allow Delphi secondary forms behind the main form
Fake modal dialog using Show?
Delphi MainFormOnTaskBar Modal windows bug

Source for Unit10:

    unit Unit10;

    interface

    uses
      Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
      Dialogs, StdCtrls;

    type
      TForm10 = class(TForm)
        btnTryDlg: TButton;
        dlgOpen1: TOpenDialog;
        btnTryForm: TButton;
        procedure FormCreate(Sender: TObject);
        procedure btnTryDlgClick(Sender: TObject);
        procedure btnTryFormClick(Sender: TObject);
      end;

    var
      Form10: TForm10;

    implementation

    {$R *.dfm}

    uses
      Unit11;

    procedure TForm10.FormCreate(Sender: TObject);
    begin
      FormStyle := fsStayOnTop;
    end;

    procedure TForm10.btnTryDlgClick(Sender: TObject);
    begin
      dlgOpen1.Execute;
    //  dlgOpen1.Execute(Self.Handle);
    end;

    procedure TForm10.btnTryFormClick(Sender: TObject);
    begin
      TForm11.Create(Self).ShowModal;
    end;

    end.

DFM for Unit10:

    object Form10: TForm10
      Left = 0
      Top = 0
      Caption = 'Form10'
      ClientHeight = 255
      ClientWidth = 414
      Color = clBtnFace
      Font.Charset = DEFAULT_CHARSET
      Font.Color = clWindowText
      Font.Height = -11
      Font.Name = 'Tahoma'
      Font.Style = []
      OldCreateOrder = False
      OnCreate = FormCreate
      PixelsPerInch = 96
      TextHeight = 13
      object btnTryDlg: TButton
        Left = 32
        Top = 24
        Width = 153
        Height = 201
        Caption = 'Try dialog'
        TabOrder = 0
        OnClick = btnTryDlgClick
      end
      object btnTryForm: TButton
        Left = 224
        Top = 24
        Width = 153
        Height = 201
        Caption = 'btnTryForm'
        TabOrder = 1
        OnClick = btnTryFormClick
      end
      object dlgOpen1: TOpenDialog
        Left = 96
        Top = 168
      end
    end

Source for Unit11:

    unit Unit11;

    interface

    uses
      Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
      Dialogs;

    type
      TForm11 = class(TForm)
      end;


    implementation

    {$R *.dfm}

    end.

DFM for Unit11:

    object Form11: TForm11
      Left = 0
      Top = 0
      Caption = 'Form11'
      ClientHeight = 183
      ClientWidth = 203
      Color = clBtnFace
      Font.Charset = DEFAULT_CHARSET
      Font.Color = clWindowText
      Font.Height = -11
      Font.Name = 'Tahoma'
      Font.Style = []
      OldCreateOrder = False
      PixelsPerInch = 96
      TextHeight = 13
    end

Answer 1

Set the modal form's PopupParent property, exactly like Remy suggested. That will parent the dialog to the StayOnTop form, which is what the dialog's Execute method is already doing. I'm not sure where Sertac's comments are coming from, but using PopupParent sets the window heirarchy correctly, so the dialog will always be above the StayOnTop form.