I am trying to write a custom WiX dialog that, as part of a workflow, displays an error image in response to certain conditions. However, WiX seems to ignore my measurements and show how it sees fit. Here is my code:
<Binary Id="WixUI_FailureImg" SourceFile="$(sys.SOURCEFILEDIR)..\Resources\Failure.ico" />
<Control Id="TestResult_Failure" Type="Icon" IconSize="16" X="15" Y="206" Width="16" Height="16" Text="WixUI_FailureImg">
<Condition Action="hide">LOGON_VALID = "1"</Condition>
<Condition Action="show">LOGON_VALID = "0"</Condition>
</Control>
I have included a snippet of the resulting dialog box below, with the original image (16x16.ico) in the background. As you can see, the image was scaled up and there is no transparency around the image. I tried 8-bit and 24-bit bitmaps, as well as icons, but they all give the same result. Is there something I'm doing obviously wrong?

UPDATE:
If you're interested in how dynamic images work, here is the relevant section:
<Control Id="TestResult_Success" Type="Icon" IconSize="16" X="15" Y="210" Width="12" Height="12" Text="WixUI_SuccessImg">
<Condition Action="hide">LOGON_VALID = "0"</Condition>
<Condition Action="show">LOGON_VALID = "1"</Condition>
</Control>
<Control Id="TestPrompt_Success" Type="Text" X="35" Y="210" Width="322" Height="10" Text="!(loc.SqlSelectDlgConnectionValid)">
<Condition Action="hide">LOGON_VALID = "0"</Condition>
<Condition Action="show">LOGON_VALID = "1"</Condition>
</Control>
<Control Id="TestResult_Failure" Type="Icon" IconSize="16" X="15" Y="210" Width="12" Height="12" Text="WixUI_FailureImg">
<Condition Action="hide">LOGON_VALID = "1"</Condition>
<Condition Action="show">LOGON_VALID = "0"</Condition>
</Control>
<Control Id="TestPrompt_Failure" Type="Text" X="35" Y="210" Width="322" Height="10" Text="!(loc.SqlSelectDlgConnectionInvalid)">
<Condition Action="hide">LOGON_VALID = "1"</Condition>
<Condition Action="show">LOGON_VALID = "0"</Condition>
</Control>
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