popupForm control size and position

procedure TForm7.WebButton1Click(Sender: TObject);
newform: TForm1;
     newform := TForm1.CreateNew(@AfterCreate);
     newform.popup := true;
     newform.Caption := 'Child form';
     newform.Border := fbDialog;


I want to show Form1 as a popup with the Top & Left +10px and Form1 to scale to 90% of the main form.
Form1 has a webImageControl that I want to fill with an image scaled proportionality.

On the webImageControl in the inspector is I set width to say 40% it scales accordingly
However if I set height to 90% the image disappears.

The images are all A4 size ( 210 x 297 ) so I need the image to scale on different platforms at 90% height and width proportionately.

I would have expected these setting to work.
HeightStyle ssAuto
HeightPercentage 90%
WidthStyle ssAuto

I replaced the webImageControl with webImageSlider and this sorted out the image size issues.