DropDownForm for STFilter (EhLib)

[DrShepard 0]

Hello! I need to set DropDownForm for MyDBGridEh.Columns[3].STFilter. My grid has 4 columns, but only one column needs to have its stfilter changed.
So I created a new class

type
  TExtSTColumnFilterEh = class (TSTColumnFilterEh)
  public
    property DropDownFormParams: TDropDownFormCallParamsEh read FDropDownFormParams write FDropDownFormParams;
  end;

How can I changed STFilter on my third column? I tried it like this
 

procedure TMainForm.FormCreate(Sender: TObject);
begin
  MainGrid.Columns[3].STFilter.Free;
  MainGrid.Columns[3].STFilter := TExtSTColumnFilterEh.Create(MainGrid.Columns[3]);
  TExtSTColumnFilterEh(MainGrid.Columns[3].STFilter).DropDownFormParams.DropDownForm := LVDropDownForm;
end;

But DropDownForm doesn't appear. 
I will be glad to receive any advice and ideas.
I'm using grid from EhLib 9.3 library.