Interesting. I had not considered that aspect and shall ponder further. Clearly the bat hitting ball involves a collision somewhat different to dropping a ball on the bat or hitting a bat with a mallet.
So how might that be worked into how you determine the optimum press?
Batted ball speed = q x Velocity of ball + (1 + q)Velocity of bat
Where q is calculated as follow q is the Bouncabilty of a bat or Apparent Coefficient of Restitution [ACoR]
Pressing is related to the willow its natural attributes, grains, volume etc and therefore the pressing pressure required, each piece of willow should be treated differently because of this. The pressing changes the elasiticity of the willow and therefore the rebound effects the willow.
As you can see ACoR being the initial multiplier this will have the biggest effect on batted ball speed . If ACoR remained constant and the ball velocity increased and the bat speed increased you wouldn't have the same increase as you would if you raised the ACoR.
There are ways of getting a really good pressing but it isn't really related to the CoR. CoR or ACoR is a product of good pressing so is batted ball speed.
So to answer your question, nothing that you mention determines the optimum pressing