Mike, when the stove is running put your hand between the stove and the stone wall. If you can comfortably keep it there and the stone is not too hot to touch you should be OK.
Understand that a dealer or a factory rep must be very conservative to protect themselves from lawsuits, and similar problems. So you will get 'owners manual' responses.
I'm not a factory rep, and I carry a large liability policy, so my advice is less 'lawyer speak' and more from experience. [insert lawyer's disclaimer here]
The stone is not combustable, it will conduct heat to combustable materials behind it, but not very well. If you have any concerns at all. I'd install a piece of sheet steel with a several-inches airspace in front of the stone, then there is virtually no chance of enough heat getting by the steel and stone to combustable materials behind.
Just some ideas from personal experiences.