Please notice the following from the FAQ:
Q: If I have a unit of 20 archers, 5 files wide and 4 ranks deep,
how many shots would I get using the Volley Fire special rule?
Would it be 15 (first two ranks plus half of the remaining models,
rounding up) or 16 (first two ranks plus half of each rank, rounding
Q: When a unit fires using the Volley Fire special rule and not all
of the unit can shoot, do you work out how many models can shoot in
the third and subsequent ranks and then halve the result, rounding
This is effectively a rules change, though. The Volley Fire special rule says half the models in each rank, which is kind of silly since this would allow a unit in one-model-wide fomation to shoot with every model in the unit. So "GO GW!", I guess.
However, you are still missing rules for picking the exact models that shoot, which is necessary to work out which models among the nebulous group of "half the models in the third and subsequent rank" are affected by range modifiers and which models are not.