[Christ]

Even without the above post, consider swirl induction. The idea is to get the mixture to move in a specific direction as it's being drawn into the cylinder, causing a secondary vacuum beyond that which the piston's movement would naturally cause. This means that only one side of the valve can be used to the greatest extent, anyway. (The area of the valve's backside that would cause flow to intersect the cylinder wall at a sharp tangent, as far from perpendicular as possible.)

This presents you with another option for increasing VE and flow at the same time, even given the apparent faults of my edited design.