Using REST to search phone numbers

I've been asked to write some stored procedures that can return data to the REST API for an integration project we're working on. The SPs should return data in XML form which will then be read and parsed by the new application. Although the SP is returning the properly formatted XML (all tags in the right place and properly indented) in Management Studio:

<cti>
  <customer>
  <matches>7192</matches>
   <customerid>1000000</customerid>
   <override>0</override>
   <name>
     <forename>Web</forename>
     <surname>Performance0</surname>
   </name>
 </customer>
 <customer>
   <matches>7192</matches>
   <customerid>1000010</customerid>
   <override>0</override>
   <name>
     <forename>Web</forename>
     <surname>Performance10</surname>
   </name>
 </customer>

... and so on, finishing:

  <customer>
   <matches>7192</matches>
   <customerid>1000100</customerid>
   <override>0</override>
   <name>
     <forename>Web</forename>
     <surname>Performance100</surname>
   </name>
 </customer>
</cti>

However, when I call the SP from the REST API the data is split into multiple <tables>:

<ExecuteLocalProcedureResults>
<Table>
<XML_F52E2B61-18A1-11d1-B105-00805F49916B>
<cti><matches>7192</matches><customer><customerid>1000000</customerid><override>0</override><firstname>Web</firstname><lastname>Performance0</lastname></customer><customer><customerid>1000003</customerid><override>0</override><firstname>Web</firstname><lastname>Performance3</lastname></customer><customer><customerid>1000004</customerid><override>0</override><firstname>Web</firstname><lastname>Performance4</lastname></customer><customer><customerid>1000005</customerid><override>0</override><firstname>Web</firstname><lastname>Performance5</lastname></customer><customer><customerid>1000006</customerid><override>0</override><firstname>Web</firstname><lastname>Performance6</lastname></customer><customer><customerid>1000007</customerid><override>0</override><firstname>Web</firstname><lastname>Performance7</lastname></customer><customer><customerid>1000008</customerid><override>0</override><firstname>Web</firstname><lastname>Performance8</lastname></customer><customer><customerid>1000009</customerid><override>0</override><firstname>Web</firstname><lastname>Performance9</lastname></customer><customer><customerid>1000010</customerid><override>0</override><firstname>Web</firstname><lastname>Performance10</lastname></customer><customer><customerid>1000011</customerid><override>0</override><firstname>Web</firstname><lastname>Performance11</lastname></customer><customer><customerid>1000012</customerid><override>0</override><firstname>Web</firstname><lastname>Performance12</lastname></customer><customer><customerid>1000013</customerid><override>0</override><firstname>Web</firstname><lastname>Performance13</lastname></customer><customer><customerid>1000014</customerid><override>0</override><firstname>Web</firstname><lastname>Performance14</lastname></customer><customer><customerid>1000015</customerid><override>0</override><firstname>Web</firstname><lastname>Performance15</lastname></customer><customer><customerid>1000016</customerid><override>0</override><firstname>Web</firstname><lastname>Performance16</lastname
</XML_F52E2B61-18A1-11d1-B105-00805F49916B>
</Table>
<Table>
<XML_F52E2B61-18A1-11d1-B105-00805F49916B>
></customer><customer><customerid>1000017</customerid><override>0</override>
firstname>Web</firstname><lastname>Performance17</lastname></customer><customer><customerid>1000018</customerid><override>0</override>

…

As you can see, a </lastname> tag has been split across the </table><table> tags and will cause problems when trying to be read by standard parsers (so I am informed). It appears that the returned data is limited to 2118 characters between the <table> tags.

Is there any way that I can get the REST API to treat my returned data like it treats data returned by one of the Standard calls (/ConstituentService/Attributes for example)?