In addition to establishing contact, the Man-Sao arm of course also has the task of protecting the body as well as possible in the process. The result is a conflict of aims: if I fully extend the arm so that the hand is as far forward as possible, I make the earliest possible contact with my opponent because my fingertips are as far away from me as they can be. This means that my elbow is raised, practically in line with my should and hand, which automatically means that the floating ribs on that side are practically unprotected.

If I keep the elbow close to my body as an alternative, however, I am protected down to hip level but my Man-Sao only extends forward by the length of my forearm. I make contact with the opponent much later and my early-warning time is much shorter.
One might be tempted to think that a position between the two extremes is best, i.e. with the elbow slightly in front of the body and the arm slightly bent, but that is not the WingTsun way. Instead we retrain the muscles surrounding the shoulder joint so that we are able to move the upper arm further forward, by extending the shoulder joint itself, so to speak. Anatomically this is not what really happens, of course: what we actually do is relax the muscles attached to the ribcage in such a way that the entire upper arm structure can be pushed forward. If correctly performed, specific movements in the Siu-Nim-Tao form produce precisely this effect over the course of time. After years of training this can be brought to the stage where actual extension of the arm is possible.

But the following happens long beforehand: WingTsun people who train accordingly are able to extend their Man-Sao just as far as if the arm were at full stretch, therefore they have the longest possible advance warning time. At the same time the elbow is low enough to give good protection to the floating ribs. WingTsun manages to reconcile the conflict of aims and combine the advantages of both alternatives while eliminating the disadvantages. Since this procedure is developed on the purely physical level, it can be directly absorbed by the subconscious mind and produce a principle resulting in the optimal course of action when needed.