HTTP Header responce problem

Good Morning,

I have an issue with some of my response headers and an irule for replacing certain responses. The rule I have below is set agains a number of our sites but when running a header response scan some of the comments don't seem to be respected. For example the "Server" and "X-Powered-By" still come back with the actual server and IIS details. Am I missing something or have I go the argument wrong?

BTW I've new with F5's and still learning how to create these syntax so appologese if I ask what seem like dumb questions, thank in advance.

when HTTP_RESPONSE {

    foreach mycookie [HTTP::cookie names] {

                HTTP::cookie secure $mycookie enable

        }

  if { !([ HTTP::header exists "X-Frame-Options" ])} { HTTP::header insert "X-Frame-Options" "SAMEORIGIN" }

  if { !([ HTTP::header exists "X-Powered-By" ])} { HTTP::header insert "X-Powered-By" "Server" }

  if { !([ HTTP::header exists "Server" ])} { HTTP::header insert "Server" "A-Server" }

  if { !([ HTTP::header exists "Cache-Control" ])} { HTTP::header insert "Cache-Control" "no-cache" } 

  if { !([ HTTP::header exists "X-XSS-Protection" ])} { HTTP::header insert "X-XSS-Protection" "1; mode=block" }

  if { !([ HTTP::header exists "X-Content-Type-Options" ])} { HTTP::header insert "X-Content-Type-Options" "nosniff" } 

  if { !([ HTTP::header exists "Strict-Transport-Security" ])} { HTTP::header insert "Strict-Transport-Security" "max-age=15768000" } 

}