fixing the blitzkrieg problem w/ HPS Nap & ACW

[BigDuke66]

Isn't the problem here the defensive fire?
I think it is triggered by unit so it can very well be that only one artillery unit fires and not the whole stack that is in the hex.
In my last game I saw often enough cavalry pass through the field-of-fire of artillery without triggering fire and even when it's only at 50%.
On the other hand there is already the cavalry fire modifier that makes fire against cavalry much more effective.