The best cause efffect analysis to explain Manny's trajectory adjustment is Epstein.
Offspeed will require more wait time. Weight shift is slowed/more weight kept on back by more back leg sit. Hand cok is prolonged (scap loading/hand hiding). As the swing proceeds the back shoulder/scap is lowered (opposite of "leveling out the swing/setting sites higher") which creates a longer more uppercutting swing which matches timing and trajectory of low/dropping pitch.
If it's a heater,he will have the weight go forward more to get the axis more upright for high ball. Shoulders will stay more level and hands will lead bathead more at contact.
For low heater, he can always drop the back shoulder a little which keeps the axis from tilting any farther forward and produces the longer more extended swing (this resembles the golf swing the most).
As Epstein explains, it's axis and shoulder tilt, not the ridiculous bend at waist thing that is key to adjusting plane and acceleration timing within plane.