As this thread (http://www.theblitz.org/message_boards/s...?tid=47923
) is closed, I had to open a new topic. I just did some quick tests to understand in more detail how the alternate fire resolution rules work.
Indirect Alternate Fire Rule
(density modifier enabled; 100% carry over of indirect fire to other units in the hex; indirect fire power *2, MP cost for indirect fire *2)
The cost (in movement points) for firing is doubled. The fire value of the unit is doubled and applied individually to every single enemy unit (hard or softt doesn't matter) in the targeted hex. Each enemy unit divides the fire value according to its own defense value, doubles it if it is in marching column, etc. Additionally, there is also a density modifier so that the effect of the fire is reduced against smaller units. For example: I had the very same artillery unit fire at infantry units in the open. Against the smaller unit (size = 60 men), the fire value was 22. Against the larger unit (510 men), the fire value was 96. Further testing would be needed to find out where the threshold is (275? 300?).
If you concentrate many units in a single hex, artillery fire will hurt a lot. Especially if your units are large. Don't waste your indirect fire on hexes that only contain small enemy units. Your fire will be relatively ineffective.
Direct Alternate Fire Rule
(density modifier enabled, 50% carry over of direct fire to other units in the hex)
When firing directly, you can still select a target unit. 100% of the fire value of your unit will be applied against that target unit. However, IF YOU'RE TARGETING A SOFT UNIT and there are other enemy units (soft or hard) present in the target hex, then these units are affected as well. It seems as if the fire against these "surplus" targets is is automatically reduced a factor of ca. 0.5. The same is true for opportunity fire, by the way. Opportunity fire will affect one unit with 100%, the other units in the hex with 50% of the fire value. (If you target a hard unit, then only the hard unit will be affected and there is no "carry over" fire to other enemy units in the hex)
In addition, all indirect fire (even the fire directed at the targeted unit) is affected by a density modifier. The smaller the unit, the bigger the loss of fire power. Again, the exact threshold when the malus starts to kick in is unkown. There seems to be no cap/limit on how big this malus can get (I've tested it up to *0.2; the targeted unit had a size of 28 men at that point). So by firing at small units, you can waste more than 80% of your potential fire power!
Smaller units are harder to kill and are usually a waste of fire power. Aim your fire at large units. Also, having many units in a single hex is bad as a portion (ca. 50%) of any direct fire directed at a unit in the hex will also affect the other units.
[Note that the density malus for firing at small units does not apply under default direct fire rules*. However, even with default rules, you can notice changes of fire values depending on the target (even if two targets have identical defence values). But it's hard to put the finger on the exact rule behind that. It's not documented in the manual. ]
*Examples for the density factor
Under default direct fire rules, I had a unit fire at an enemy unit which had a manpower of ca. 250 men. My unit's fire value was 260. Then I had the same unit fire at another enemy unit (same defence and cover as the other unit...) which had a manpower of ca. 70 men. My unit's fire value was the same: 260.
Under alterante direct fire rules, I had the very same unit fire at the same units. My fire value against the larger unit (260 men) was 238. So there is a slight loss of fire power. This loss was even more pronounced against the smaller unit, against which I only had a fire value of 117.
I also want to point out that I don't know how combined units are treated when the density modifier is active. I guess it's better keep units split-up so that they're smaller and profit from the density malus. On the other hand, combining units is still a means for deception, for misleading the opponent about your real strength.
Generally, these are very powerfull rule-changes which can significantly shift the balance of scenarios. Especially fully stacked hexes (--> at objectives) can be broken up more easily by artillery if the alternate indirect fire rule is active. If there are no supply sources in a scenario (so that ZoC/isolating is not that important), these rules can be a means for designers to keep forces fluid and spead-out a bit more.