Manual clarification - HPS/JTS Napoleonic series

[BigDuke66]

While trying to understand the various modifiers I did already stumble over these -50% in automated defensive fire and I simply couldn't explain where they came from, so what is mentioned there seems to be the only explanation, at least the only I got until now.

I just made a fast test and triggered defensive fire from a 646 men strong 3-rank line formation with muskets on 1 hex range on an infantry unit in column.
Fire value shown was 1513.
Now my calculation is:
646(men) * 5(musket fire value) = 3230
3230 * 0,75(Fire value adjusted to 3-rank line formation, they fire with 75% effectiveness) = 2422,5
2422,5 * 0,5(automated defensive fire gives 50%) = 1211,5
1211,5 * 1,25(fire on infantry in column) = 1514
I guess somewhere along the calculation the values were rounded up or down so thats why I'm 1 off the actual result.
So either the -50% also count here or I totally miscalculated.

PS Maybe an optional rule that is used in the Civil War series were you can set 100% defensive fire would be nice.