How Do You Set A Default Size Of A Control That You Can Resize?

How do you set a default size of a control that you can resize?
I have been looking at a code sample from Charles Petzold.
It is from here:

http://forums.xisto.com/no_longer_exists/
it uses mouse over methods to increase the size of button classes.
I have it working but I want to make some modifications. I want the starting size of the button to be larger. I do not know how much of the code I need to post here to make the issue clear enough. The XAML for the page describes a "FisheyeButton" that is described in a seperate xaml file. Something like this:

<StackPanel x:Name="LayoutRoot" Width="1017" Orientation="Horizontal" Height="253">  	<src:FisheyeButton Style="{StaticResource btnStyle}" ButtonContent="Button No. 1" />  </StackPanel>

The functionality of the project is such that if I give the Fisheyebutton a width and height a set size at this loction, the effect where the size of the control the effect of becoming larger does not happen. In other words, if I write in the <src:FisheyeButton... tag above Width="100", then the button does not behave at run time as it should.
In the same page.xaml file, the btnStyle is defined like this:

<UserControl.Resources >   <Style x:Key="btnStyle" TargetType="src:FisheyeButton">	  <Setter Property="VerticalAlignment" Value ="Center" />	  <Setter Property="HorizontalAlignment" Value ="Center" />	  <Setter Property="FontSize" Value ="12" />   </Style ></UserControl.Resources >

I wonder if perhaps at this point, I can add a "Setter" property to define a default starting widh and height for the class.
The animation, what makes the custom button class grow larger and also return to a normal size, is done in a seperate XAML for the Fisheyebutton class:

<UserControl x:Class="FisheyeButtons6.FisheyeButton"			 xmlns="[url="http://forums.xisto.com/no_longer_exists/;			 xmlns:x="[url="http://forums.xisto.com/no_longer_exists/;			 xmlns:vsm="clr-namespace:System.Windows;assembly=System.Windows"			 xmlns:src="clr-namespace:FisheyeButtons6"			 mc:Ignorable="d"			 xmlns:d="[url="http://forums.xisto.com/no_longer_exists/;			 xmlns:mc="[url="http://forums.xisto.com/no_longer_exists/;			 d:DesignHeight="64" d:DesignWidth="146">	<Grid x:Name="LayoutRoot" Background="White" >		<vsm:VisualStateManager.VisualStateGroups>			<vsm:VisualStateGroup x:Name="CommonStates">				<vsm:VisualState x:Name="Normal">					<Storyboard>						<DoubleAnimation Storyboard.TargetName="presenter"										 Storyboard.TargetProperty="ScaleX"										 To="1" Duration="0:0:0.25" />						<DoubleAnimation Storyboard.TargetName="presenter"										 Storyboard.TargetProperty="ScaleY"										 To="1" Duration="0:0:0.25" />					</Storyboard>				</vsm:VisualState>				<vsm:VisualState x:Name="MouseOver">					<Storyboard>						<DoubleAnimation Storyboard.TargetName="presenter"										 Storyboard.TargetProperty="ScaleX"										 To="3" Duration="0:0:1" />						<DoubleAnimation Storyboard.TargetName="presenter"										 Storyboard.TargetProperty="ScaleY"										 To="3" Duration="0:0:1" />					</Storyboard>				</vsm:VisualState>			</vsm:VisualStateGroup>		</vsm:VisualStateManager.VisualStateGroups>		<Button>			<src:ScalableContentPresenter x:Name="presenter" />		</Button>	</Grid></UserControl>