thinkpad - Behavior of Windows 7 power options (Sleep, then hibernate)

I have my Lenovo X220 running Windows 7 Pro configured to (on battery):
1. Sleep after 20 minutes
2. Hibernate after 45 minutes

However it seems like whenever I leave my laptop for a long period, I find it has totally drained the battery and shut off.

I can invoke a hibernate from the start menu, so that capability is enabled.

Is Windows not capable of invoking a Hibernate from within the sleep state? The FAQ implies otherwise:

http://windows.microsoft.com/en-US/windows7/Sleep-and-hibernation-frequently-asked-questions

Will sleep eventually drain my laptop battery?
Sleep requires an extremely small amount of power. If your laptop battery charge gets critically low while the computer is asleep, Windows automatically puts the laptop into hibernation mode.

So, technically, the above statement could be true, perhaps only the critical battery level event can wake the machine from sleep to invoke hibernation (as opposed to the Hibernate after minutes setting, which I am trying to use).

Perhaps the Lenovo power manager is overriding the Windows one? Looking in the Lenovo power manager, I have no idea how one tells if it is "active", if it is overriding windows power management, etc.