A320 stall audio warning at high altitude
I was teaching stalling recently in an A320 sim. We were at FL 350, clean, normal CG, GW about 58 tonnes, ALT Law (via FACs off). In level 1g flight we had to drop about 15 kts into the Vsw red/black strip before we got the ‘Stall, stall’ audio. During this time we were flying normally, around 7 degrees pitch. I had expected the audio to trigger as we entered Vsw, as it does at low level, certainly not as late as -15kts. I would have put it down to a sim problem, but then just about the same thing happened a couple of days’ later in a different sim.
I cannot find any relevant reference in the Airbus FCOMs, FCTM, or other documentation. There are merely rather vague allusions to the audio warning being triggered at an 'appropriate' time before the stall.
Am I missing something important about high alt stall warning? I'd be most grateful for any guidance.