As per Darin Morgan; velocity, velocity, velocity.
In addition, any porting should also involve increasing swirl. This is mixture motion. A tight quench like 0.025" is another aid. Combine that with Somender Singh grooves to direct compression air/fuel coming out of the quench to aid swirl and toward the spark plug. Brian Salter described this in a Live with David Vizard and Andy Woods. Building as high compression in as possible and use water injection to control detonation. Distilled water with 2% water soluble oil. Methanol is to prevent freezing.