You're right, Nik. The shoulders is the curved line/area connecting the sides to the top. And you're also right, that #52 has very slight taper - and so do the others I mentioned. Nevertheless #52 is the most straight/square/full block, I know of.
Right, #52 is regarded as the most straight block type. For the others, there's a fine thread on block shapes with posts by Josh, I'm trying to dig it up.