D800E with Speedlight SB-910

Maybe somebody can answer this question:
I have set my custom settings such that when I half press the shutter release the camera will auto focus as well as light meter; C1=ON.
I find this very useful, especially when I want to re-frame the shot but maintain focus and proper exposure of the original object, for example a face. This is all working well and easy to understand. Now add to this the built-in, or the SB-910, flash and all is well and easy to understand as long as I do not re-frame the shot. However, shooting as described above with flash and re-framing the shot I do not understand how the D800-SB910 achieves proper exposure since it does not fire a pre-flash before I re-frame.
1. Does it simply ignore the initial light metering and do a normal pre-flash - meter - flash exposure in the new location.
2. Or does it use the initial light metering, without a pre-flash, to calculate required flash-lumens to achieve desired exposure of the object selected before re-framing.

You are right that TTL flash exposure depends on preflash, but the TTL flash system is always two exposures, one for the ambient light, and one for the flash. A double exposure, so to speak. Ambient light might be insignificant level sometimes, but there are always these two factors.

In Auto modes (A, P, S), the ambient light reading sets the shutter speed or aperture for the ambient light exposure. Then slightly later, the separate TTL metering fires and meters the preflash, and sets the flash power level for that aperture it discovers is being used.

TTL BL mode exposure tries to balance (reduce) the flash level to fit in with the ambient exposure, where TTL mode exposure ignores ambient, and gives full working flash value regardless of any ambient situation.

If you want to meter TTL flash in one area, and then move the camera and take the picture in another area, using the previous exposure metering, then the FV Lock feature does that (meters the flash value and holds it until shutter button is triggered). However, it is most useful to bypass getting pictures of the subject blinking from the preflash (and/or commander signals).