Two questions that have been nagging at me...

1) Why do engines perform better with combustion 'focused' under the exhaust valves (like what's done with the Roller Waves)?

2) If combustion isn't taking place on the exhaust side (more in the center of the chamber), what would the ideal shape of the cumbstion chamber be in our motors (or in pent-roof engines in general, particularly those with large quench pads (Y8/GSR heads)?
What shape would be ideal if it was taking place on the exhuast side?

Ideal would be what would be the most ideal piston design, and the head/chamber would be a B18C1/GSR head.

Anyone care to help me out..?