My understanding is that the combining of multiple shots by the software has the added side effect of essentially halving the ISO for each additional shot. I forget where I read that. Might have been from Fred himself.
So at 16 or more shots, even with ISOs around 6400, you're getting an effective ISO of 100.
charles.K wrote:
I was experimenting this evening with the SR app in Custom mode with 128 shots RAW for low light high ISO shots.
I was using a still flower arrangement from earlier with the A7rII and GM 85 @ f/1.4 and 6400 ISO. The room had no light just lighting ambient in other rooms. With PP'ing I could not see any noise in Lr. What I did find unusual was how the WB was behaving quite differently.