Slitherine

If you have a unit of 4 cavalry in two ranks each of 2 bases. One enemy unit is in front of one of the cavalry front rank bases and another enemy unit is in front of the other front rank base. So each of the cavalry front rank bases must shoot at the enemy to the front. The target priority says that the second rank must follow the same target priority as the front rank. Thus there is one front rank and one rear rank shooting at each enemy unit. QED only 1 dice at each and only 2 in total. Is that correct or does the shooting unit get a total of 3 dice and chooses at which enemy unit it throws 2 dice?
And if so how is this justified?

Shooting dice is per target, so one dice on each target. If you have 1 and a rear rank shooting from a BG they could combine with 1 and a rear rank from another. It then gets complex with different POA's, shooter quality, etc, but they are taken as worst for those combining to make a dice.

Two dice is correct, the rear rank is wasted.