IMHO its better to test for text/html to report a possible XSS, there are a more content types that could cause reflect the content and dont have a XSS. like javascript, css, plaintext files, etc.
Fine tuning the template. Sometimes a host will redirect the original request to another page or subdomain and the XSS happens on that page instead of with the original request. I believe a max-redirects of 1 should be sufficient.