Bolty,
The "feel" for the Lo and Med settings are to stop the A/B system instantly trying to attain x.x m/s/s decell, but rather give it a smooth transition.
I recall (but can't find a reference) a WoW nose wheel requirement for MAX to occur, but can't find a reference. Certainly when I saw it in the sim last there is a delay until the nose wheel is down.
Off topic, <since you seem to know a bit about it> are you sure they use Mg and Al alloys in the region of the wheels/brakes? I could see Ti/Co/Ni alloys, (or maybe Mn at a stretch) but Mg and Al just doesn't add up to me. Happy to be told otherwise, but what little I do know about high alloy metallurgy makes it difficult to grasp your statement.