Sounds like you are talking about two separate things as if they are one. There are two failsafes:
1. The NAZA's built-in failsafe
2. Your transmitter/receiver's failsafe
The NAZA's built-in failsafe is triggered by a switch on your transmitter.
Your transmitter/receiver's failsafe is triggered when the radio signal is lost between the transmitter & receiver.
NAZA Failsafe
As far as the NAZA is concerned, the "switch activated" failsafe completely ignores what you are doing with the sticks or any other switches or buttons. When the pilot flips the switch, the NAZA goes into its built-in failsafe mode. The pilot no longer has command of the NAZA - it takes over complete control and ignores all other commands. The multi will descend until it lands, regardless of whatever the pilot is doing with the transmitter.
Transmitter/receiver Failsafe
When you mention the throttle, you are talking about is the transmitter's failsafe. That is, when the onboard receiver loses signal from your transmitter, what instruction does the receiver send to the NAZA. This is completely different and separate from the NAZA's failsafe. What your receiver can tell the NAZA to do depends on your receiver's capabilities. Some can only be preset to give a throttle signal, some can be preset to give any signal you want.
From what you posted, it seems that your receiver can be programmed with a preset throttle failsafe. If that is your only option, then I'd guess you want the throttle to be at about 25-30% for a slow landing. With this setup, the NAZA will not be using its own failsafe, it will just think that you are telling it to descent at a certain throttle input. The actual throttle level you'd want will depend on your frame, batteries, props, etc. I'd say 25-30% is probably a good place to start, but once you have your multi built and flying, you should do some tests to pick out the correct value for your multi.
If your receiver has 'preset failsafe' capability, then you could simply have the preset engage the NAZA's built-in failsafe. This is how my transmitter & receiver are setup. If the receiver loses signal, it "flips the switch" and activates the NAZA's built-in failsafe feature. I think this is the better of the two options.