Posture, not pose.
Alphonse and all the other warforged, are squattish, with a very similar ratio between torso, arms, shoulders and legs. No human being could wear the armor that is Alphonse's body and still have human-like proportions. The proportions are quite similar in the warforged, who are also portrayed as squattish. Specially when the 'forged in question has Adamantine Body.
It's been asked "how could they be different". In more ways than they could be similar. From the Cylons to C3PO, from Battle Chaser's Calibretto to Iron Kingdom's war golems, there are litterally countless ways that a "sentient suit of armor" could be made different from the 'forged or Alphonse.