Exclude response from assertion in Ready API Secure

Hi,

I assume this is where I should ask questions about Ready API Secure. 

I want to add exclude a 413 error from showing an error. In the XML Bomb section the response is:

HTTP/1.1 400 Bad Request
Cache-Control: private
Server:
Date: Wed, 22 Apr 2015 23:57:23 GMT
Content-Length: 0

When I add a "Valid HTTP Status Codes" assertion for 400 I STILL see the above assertion. It's as if somewhere else it is flagging it as bad.

Any ideas?