Here's the answer. Street Magic, p. 160, "Note that full body armor does not "conceal" the person within and prevent them from being targeted." A person, 100% clear answer with no rationalization. Why does full body armor not conceal you from magic? Because the rulebook says it doesn't.
And does the rulebook make sense? No, it does not. It says that Non-Living things show up on the astral
Any non-living objects
appear as faded semblances of their physical selves, gray and lifeless,
while the auras of living things are vibrant and colorful.
Non-magical and non-living objects have only gray, lackluster
shadows rather than auras, but pick up impressions from being
in contact with living auras.
both from page 191 Shadowrun 4A. If a lightbulb was contained within a box made of four inch thick steel, the light emitted from it would not be visible from outside of the box nor would the bulb be visible, excluding the addition of a camera to the inside of the box. If an animal was placed inside of the same box, it would not be visible from the outside of the box. It would not be targetable by direct spells. There is no logical reason that the fact an item is being used for the purposes of armor and protection that it magically allows whatever is inside to be targetted from the outside. If that was the case, you would be able target people hiding inside of a concrete bunker twenty feet thick simply because you can see a corner of the building. The bunker covers your entire body from the outside world, and is being used as full body armor, so by the logic of the rules it doesn't make any sense.
In any games I were to run, or any game I was to play in, I would either change the rules or talk to the DM and houserule it because otherwise it makes absolutely zero sense. It might not be the rules as written, but it makes no sense otherwise.