Regarding the issue of item sizes interfering with each other across different tabs.

[#1]

As shown in the JSL, the graph size is limited by the third tab and cannot be reduced further. This may be because the page of the third tab cannot be minimized any further. However, if I want to continue to shrink the graph size while keeping blank space in other areas of the page, how can I resolve this interference between different tabs?

Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
NW = New Window( "Test Window",
	tb = Tab Box(
		tabPage0 = Tab Page Box(
			Title( "Test Tab 0" ),
			ObTab1 = Outline Box( "Tab 0", 
				Ob0 = Outline Box( "Test Graph 1",
					GB0 = Graph Builder(
						Size( 534, 80 ),
						Show Control Panel( 0 ),
						Variables( X( :age ), Y( :height ), Y( :weight ), Overlay( :age ) ),
						Elements(
							Position( 1, 1 ),
							Points( X, Y, Legend( 4 ) ),
							Smoother( X, Y, Legend( 6 ) )
						),
						Elements(
							Position( 1, 2 ),
							Points( X, Y, Legend( 5 ) ),
							Smoother( X, Y, Legend( 7 ) )
						)
					)
				);
			), 
		),
		tabPage1 = Tab Page Box(
			Title( "Test Tab 1" ),
			ObTab1 = Outline Box( "Tab 1", 
				Ob1 = Outline Box( "Test Graph 1",
					GB1 = Graph Builder(
						Size( 534, 450 ),
						Show Control Panel( 0 ),
						Variables( X( :age ), Y( :height ), Y( :weight ) ),
						Elements( Position( 1, 1 ), Points( X, Y, Legend( 4 ) ) ),
						Elements( Position( 1, 2 ), Points( X, Y, Legend( 5 ) ) )
					)
				);
			), 
		), 
		tabPage2 = Tab Page Box(
			Title( "Test Tab 2" ),
			ObTab2 = Outline Box( "Tab 2",
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),  
			), 
		), 
	)
);

[#2 · Accepted solution]

You just have to turn "Fit to Window" off.

Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
NW = New Window( "Test Window",
	tb = Tab Box(
		tabPage0 = Tab Page Box(
			Title( "Test Tab 0" ),
			ObTab1 = Outline Box( "Tab 0", 
				Ob0 = Outline Box( "Test Graph 1",
					GB0 = Graph Builder(
						Size( 534, 80 ),
						Show Control Panel( 0 ),
						Fit to Window( "Off" ),
						Variables( X( :age ), Y( :height ), Y( :weight ), Overlay( :age ) ),
						Elements(
							Position( 1, 1 ),
							Points( X, Y, Legend( 4 ) ),
							Smoother( X, Y, Legend( 6 ) )
						),
						Elements(
							Position( 1, 2 ),
							Points( X, Y, Legend( 5 ) ),
							Smoother( X, Y, Legend( 7 ) )
						)
					)
				);
			), 
		),
		tabPage1 = Tab Page Box(
			Title( "Test Tab 1" ),
			ObTab1 = Outline Box( "Tab 1", 
				Ob1 = Outline Box( "Test Graph 1",
					GB1 = Graph Builder(
						Size( 534, 450 ),
						Show Control Panel( 0 ),
						Fit to Window( "Off" ),
						Variables( X( :age ), Y( :height ), Y( :weight ) ),
						Elements( Position( 1, 1 ), Points( X, Y, Legend( 4 ) ) ),
						Elements( Position( 1, 2 ), Points( X, Y, Legend( 5 ) ) )
					)
				);
			), 
		), 
		tabPage2 = Tab Page Box(
			Title( "Test Tab 2" ),
			ObTab2 = Outline Box( "Tab 2",
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),
				Button Box( "Test", ),  
			), 
		), 
	)
);

[#3 · Accepted solution]

Fit to Window is what you should do in this case (like suggested). Sometimes you might need to 

<< Set Auto Stretching({0,0});

on some of the display boxes. In this case you could use it on tabPage0 and tabPage1 for example