QGridLayout scaling widgets

[Markus_AC]

I'm having a problem about the scaling of widgets in a QGridLayout.
I have a layout with 7 rows and 1 or 2 columns. There is a header in row 0.

Then after I want to put a widget in row 1 (only 1 column) and a QwtPlot and a QLabel in row 2. And so forth in the next rows. I do not select any fixed height for my QwtPlot widgets and QLabels (in rows 2, 4 and 6). My pheader and the widgets in rows 1, 3 and 5 have a fixed width.

QGridLayout *layout = new QGridLayout(this);
	if(layout != 0)
	{
		layout->addWidget(pheader, 0, 0);
		layout->addWidget(topWidget, 1, 0);
		layout->addWidget(topGraph, 2, 0);
		layout->addWidget(topGraphLabel, 2, 1);
		layout->addWidget(midWidget, 3, 0);
		layout->addWidget(midGraph, 4, 0);
		layout->addWidget(midGraphLabel, 4, 1);
		layout->addWidget(botWidget, 5, 0);
		layout->addWidget(botGraph, 6, 0);
		layout->addWidget(botGraphLabel, 6, 1);
	}
 
	setLayout(layout);

QGridLayout *layout = new QGridLayout(this);
	if(layout != 0)
	{
		layout->addWidget(pheader, 0, 0);
		layout->addWidget(topWidget, 1, 0);
		layout->addWidget(topGraph, 2, 0);
		layout->addWidget(topGraphLabel, 2, 1);
		layout->addWidget(midWidget, 3, 0);
		layout->addWidget(midGraph, 4, 0);
		layout->addWidget(midGraphLabel, 4, 1);
		layout->addWidget(botWidget, 5, 0);
		layout->addWidget(botGraph, 6, 0);
		layout->addWidget(botGraphLabel, 6, 1);
	}

	setLayout(layout);

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It is strange that the widgets in row 4 are larger (in height) than those in row 2 and 6, but all should be of the same size.

Before this I used a QVBoxLayout, because I didn't have the QLabel behind the QwtPlot, and all QwtPlot-Widgets had the same size.

What can I do to make the QwtPlots to equal size?