Good question. All Ultra Fast Boot (UFB) does is skip some POST operations, which does not seem to be happening in your case. There is even a new ASR utility program that must be run to get into the UEFI when UFB is enabled. Given your 13 second POST, where you can no doubt get into the UEFI, UFB does not seem to be working.
Could it be that Win 8 RTM is the cause, since I read there have been updates between RTM and the final public release.
I tried setting that option to Fast, with Windows 7 on two SSDs in RAID 0. That seemed to cause a double POST, and was slower than usual. Set it to disabled and it seems faster than ever.