VNX2 Hot sparing rules

I'm curious if anyone has any direct experience with this because I've heard a lot of contradictory things.

When the VNX2 chooses a hot spare, from the MCx whitepaper, it goes through 4 steps seemingly in this order:

1. Drive type

2. Bus

3. Size

4. Enclosure

What is unclear to me (and this is where I've heard conflicting info) is whether #2 Bus actually takes priority over #3 size. 

So for example, say I have a 600GB hotspare on bus0, and a 900GB hotspare on bus1.  On bus1, I lose a 600GB drive.  Which hotspare will be invoked?  Since hotsparing is now permanent, I would hope that it is the 600GB hotspare on bus0, but the whitepaper seems to indicate otherwise.