i did reduce their attack timers, and they also shoot a "Detection beam" in the oppisite direction of where they are looking. so its possible they just choose "idle" in their behaivour over and over and not detect you because their against a wall ect.
I've spent a few minutes with each of the wendigos to see if any of them would detect me, but none ever did anything but continue to walk around. For reference, I tested this with a couple of wendigos outside of Wendigo Point and both of them worked properly.