[Henry Schmidt]

All high quality pistons are both cam ground (wider at the front and back, narrow at the pin) and barrel ground (smaller below the ring land, larger at the middle of the skirt and narrow again at the base of the skirt). All of this is designed to reduce piston slap (keep the piston from rocking) and friction (reduced contact area).
Back in the early GP days, Honda developed an oval piston and cylinder combination to exploit these very principles.

The first JE pistons were not barrel grounds and the result was a huge clearance issue. It wasn't until they purchased the proper tooling that their product became usable in air cooled engines like Porsches. A lot of the stories you hear about JE are left over from those days some 15 years ago.