There may be a good reason for the size difference of the original jockey compared to this new one. I doubt Ridley would overlook such a huge detail, especially when the jockeys seat is obviously too big for this smaller Engineer. Maybe the Engineer grows in size... maybe the Jockey and the Engineer are two different characters with different roles... maybe the Engineer is a mutated human, much different than the Jockey??
My point is:
There are too many maybe's... JUST CHILL OUT and wait for the film! Theres no sense in building this up when the movie is only weeks away from being release. I swear, I feel that some of you go out of your way to ruin these movies for yourselves.