This is not my understanding. My understanding is that low-speed and high-speed conflict, and you MUST TAKE high-speed auto brake to get ACC.
This is ALSO not my understanding. Where did "37 MPH" come from? My understanding is that the low-speed system is specifically for that: low speed. It uses the the lane-keeping camera plus the ultrasonic parking sensors to keep you from running into things like walls when you're getting into parking spaces or hitting tricycles you haven't checked for. This is in addition to the beeping as you approach things, and all it does is slap on the brakes when the parking beeps would normally just become a solid tone.
The high-speed auto-brake and ACC systems adds radar. Based on a video posted somewhere here a few months back (which hasn't been easy to refind), it monitors vehicles ahead and one lane to either side. It uses the relative speeds of these things to establish what is a vehicle vs what is a bridge abutment, etc. If you're driving at 50 and approaching a thing at 50, it assumes the thing is a fixed object and not moving, and you as driver will avoid it. If you're driving at 50, and approaching a thing at 35, it assumes the thing is a car and pays attention. It also uses a forward-facing camera to establish what's IN your lane vs what's not in your lane, and both must be working correctly for ACC to turn on (along with the brake pedal, but that's another issue). The high speed auto brake fires whenever you're going to otherwise hit something that looks or tracks like a car, regardless of whether ACC is on or off, but isn't promised to prevent a collision, because there's too much variable to make such a promise. The ACC ONLY cares about other vehicles, when it's turned on, and tries to match the set following gap ONLY behind vehicles in your lane. It uses the same input devices as the auto-brake system, but they're not the same and that's why they're listed as separate features.
Yes.
