Connection keep-alive

bonjour
l'outil webpagetest.org me dit que j'ai des problèmes de

Use persistent connections (keep alive): 41/100

FAILED - http://www.xxx.com/boutique/index.php?cPath=200000_230000_230200_230239
FAILED - http://www.xxx.com/boutique/includes/stylesheet.css
....
Dans $_SERVER je vois [HTTP_CONNECTION] => Keep-Alive.
J'en déduis que les connexions Keep Alive sont possibles sur le serveur mutualisé

Dans mon fichier htaccess sous la racine du site, j'ai bien
<IfModule mod_headers.c>
Header set Connection keep-alive
</IfModule>

requete :
GET /boutique/index.php HTTP/1.1
Host: www. .com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:43.0) Gecko/20100101 Firefox/43.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: fr,fr-FR;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Referer: http://www .com/index.php
Cookie: __utma=77174151.1155216490.1437657198.1437657198.1453212615.2; __utmz=77174151.1437657198.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=fudedaga7nhreu1sic3sntp26
Connection: keep-alive

Reponse;
HTTP/1.1 200 OK
Date: Thu, 11 Feb 2016 14:20:04 GMT
Server: Apache
X-Powered-By: PHP/5.6.17
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Vary: Accept-Encoding,User-Agent
Content-Encoding: gzip
Connection: keep-alive, close
Content-Length: 4818
Content-Type: text/html; charset=UTF-8

question : ai je bien un probleme de persistence connection??? Si oui que puis-je faire pour le résoudre??
Merci