How to Specify the Size of Rectangles in a figure?

I have drawn 3 rectangles and put them in a struct as follows. It occupies the whole figure1 area. How to make them so small that just, for example, these rectangles just take one fifth of the figure1’s area?

hfig = figure;
for i = 1 : 3
    W = 4;
    X = i.* W;
    Y = 0;
    H = 8;
    R = rectangle;
    R.Position = [X Y W H];
    G(i).r = R;
end

Answer 1

[Jan]

The rectangle is a child of an axes object. The axes is fit to the included data automatically, if you do not specify its data limit.

hFig  = figure;
hAxes = axes('NextPlot', 'add', 'XLim', [0, 20], 'YLim', [-1, 10]);
W = 4;
Y = 0;
H = 8;
for i = 1 : 3
  X = i.* W;
  R = rectangle;
  R.Position = [X Y W H];
  G(i).r = R;
end

[Rightia Rollmann]

Thanks, but still one problem:

How can I define the struct G as the child for figure? Further information here.