Custom Fields do not work in the SI List View web part. Take the example from the help file below, try and concatenate any two fields using the syntax provided and there is no output at all.

For example, to display a full name, you can concatenate the first name and last name as follows:

<Field Name=CalculatedFullName Title=Full Name CalculatedValue=&amp;lt;%First Name%&amp;gt; &amp;lt;%Last Name%&amp;gt; />