Glueball
I can't remember what range scale was set. As I said earlier, both myself and the skipper have had experience of military traffic disappearing and popping up with the switching on and off of the TCAS. The fact that we were over Iraq, speaking to a controller who appeared to be unaware of the conflicting traffic, and aware that TCAS is only of use if the other a/c has it switched on, was enough to convince us both that it would be prudent to take proactive measures. Like I said, maybe not what the book says, but definitely on the safer side..
There may also be a bit of conditioning involved-on my last sim check we had to practise RAs, one of which was traffic dead ahead descending to our level. We had to react on the RA. Say what you like, in that situation when the RA is triggered it's fairly dramatic.