CADad,
Well, I tried to see how low I could get, and established that at my age, it is an uncomfortable position! But the best I could do was 4 ft above the ground. I really don't think that even Tom Terrific could launch a 4 seamer from 3 ft above the ground.
The figure of 16 ft/s^2 is twice as high as Adair's estimate of 1/4th of gravity. Furthermore, Briggs used a vertical wind tunnel to show that the drag at 95mph is equal to the force of gravity. It is very hard for me to believe that half of the total drag can be directed perpendicular to the direction of motion.
Most MLB baseball parks have cameras located near 1st and 3rd base. These are well positioned to show the track of a pitch in a vertical plane. I strongly believe that if any pitcher were even close to producing a "rising fastball", we'd be seeing it on broadcasts.
Finally, I'm puzzled by the idea that high fastballs react differently than low fastballs. The aerodynamics should be very similar, and the deviation from the initial trajectory should hardly differ. I think batters swing at high fastballs because they expected or perceived a slower or downward breaking pitch.