Secondary XML Index not being used in query plans

I have a question regarding XML indexes.

We have a table OVERLAY_ITEM_SEARCH_XXX with almost 5 million rows. The table has 2 columns – an identity column (bigint) and a SEARCH_VALUES column (XML). The XML column has a primary XML index and secondary XML PATH index.

The SEARCH_VALUES XML column contains a number of fields under the ATTRIBUTES node, e.g. SECTION_REF, but these are variable, as they are derived from user configuration.

The elements c121 and o870 represent client_id = 121 and overlay_id = 870. There are several clients and overlays within the database.

So a typical SEARCH_VALUES XML value for a particular row may look like this:

<c101>

       <o777>

              <SECTION_REF>1/2/567</SECTION_REF>

              <NAME>FRED</NAME>

<POSTCODE>W1 21A</POSTCODE>

       </o777>

</c101>

Performing the following 2 queries, for which no rows are found

1. A TOP 1 query

selectTOP 1 * from overlay.OVERLAY_ITEM_SEARCH_XXX s

where s.SEARCH_VALUES.exist('c121/o870/ATTRIBUTES/SECTION_REF/text() [contains(.,"J1")]') = 1

2. A SELECT * query

select*from overlay.OVERLAY_ITEM_SEARCH_XXX s

where s.SEARCH_VALUES.exist('c121/o870/ATTRIBUTES/SECTION_REF/text() [contains(.,"J1")]') = 1

The  ‘SELECT *’ query utilises the secondary XML index and runs in 9s, whereas the ‘TOP 1’ query doesn’t use the secondary XML index an takes 100s.

Why does the TOP n query not utilise the secondary XML index? N.B. This is from the actual query plan.

It seems that any query we try other than "select *" fails to use the index, e.g. IF EXISTS(SELECT *...)

Does anyone have any similar feedback from using XML indexes on large tables?

Note that the search for the searchable value (e.g. in the example above ‘J1’), needs to be a ‘contains’ type search.

This is using SQL Server 2012 SP2

Any help/comments would be appreciated.