Space Jockey in the trailer looks like human size

Not only too small, but design characteristics and proportion are off when compared side by side. Detail discrepencies on the chair and SJ could correspond with each other if either the small SJ grows into the larger size as it activates or morphs with the ship upon activation. Or, it could be the small blue dude gets out of the suit, as seen in the trailer, and a larger infected creature gets into the chair and morphs into the chair. These two explanation could be plausible, considering the advanced life forms' technology. Someone else had suggested that the suit itself is biomechanical and alive. Perhaps a living being activates the chair/devices/ship?

I think the arms and head are thicker, not shorter- because they are covered in flesh. Same with the ribcage. Skeletal remains would look longer and more slender, not to mention would be collapsed inward without tissue to keep them separated. Personally, I have yet to see anything that shows an SJ as being the same size as a human. There is a figure standing in front of Shaw while she is down in a corner, but his face is out of frame. I think that is a mutated Halloway. He may in fact eventually end up in the chair, but there are two engineers (or at least two individuals) in the chair room in the last trailer. As the engineer turns and stands, the others arm and shoulder are visible.