FTTB problems

[seog]

Hi

Before of configure cdn my first byte was 1.2s but now I have cdn configured to improve first byte time and it is 2.375s
I don´t understand why other cms prestashop have 0.200s of first byte time when I have 2.375s with the next settings:

-Pagespeed 99/100
- IMG in sprites from subdomains
- CSS and JS load from subdomains
- Memcache enabled
- Gzip enabled
- 2GB in VPS
etc..

http://www.webpagetest.org/result/13...
Do you see something wrong with my web that generates this hight FTTB ??

Thanks and best regards