Hi David,

I can suggest you to find reference to html element which represents ContentPane of webtab and set its minHeight. That element has id tab.ClientID+'_cp'.
Below is example for you.

  <script type="text/javascript">
  function initTab(webTab)
  {
   var cp = document.getElementById(webTab.ID + '_cp');
   cp.style.minHeight = '200px';
  }
  </script>
  <igtab:UltraWebTab ID="UltraWebTab1" runat="server">
   <ClientSideEvents InitializeTabs="initTab" />
   <Tabs>
    <igtab:Tab Text="New Tab">
     <ContentTemplate>
      <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
     </ContentTemplate>
    </igtab:Tab>
    <igtab:Tab Text="New Tab">
     <ContentTemplate>
      <div style='border:1px solid red;background:orange;width:400px;height:400px;'></div>
     </ContentTemplate>
    </igtab:Tab>
   </Tabs>
  </igtab:UltraWebTab>