Update: - Units defending in Melee fire at 100% fire ??

[Mowgli]

My experience differs quite a bit - I suppose it's because you play with the "column pass through" optional rule disabled? I play with "column pass through" enabled and no phases. Closing in frontally against enemy artillery batteries over distances longer than a single turn's movement is total suicide with my current settings. I've seen two artillery batteries on their own beat back attacks by a line of 6 battalions. 

It's true that the losses inflicted by artillery opportunity fire rarely cause disruption. However, the fire inflicted by artillery OFFENSIVE fire on medium or close ranges will inflict horrible losses to ALL units in the hex (if "column pass through" is enabled) and easily rout AT LEAST one of the units (ALL need to test for the morale check, not just one), causing disorder to the rest, which in turn makes the whole attack fail (attacking while disordered troops gives a -66% assault power malus). I've seen stacks of 3 battalions suffer 200+ casualties from a single artillery opportunity fire action at point blank range. Just saying. 

So, I guess I will just play without "column pass through" in the future. Artillery is already op right now with this optional rule, and it becomes even stronger with 100% opportunity fire vs. assaults.

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When it comes to infantry, I'm totally in favour of greater defensive firepower. But I don't think the +50% on opp. fire will make any difference - it will hardly suffice to cause disruption.

Nope I use almost all rules, and this one is one of them. I believe that this is the point of this rule to stop full stacks in open areas. I think this is completely justified. Since in order for the morale check, you need to be unable to reach the battery in one turn - thus the enemy will shoot at full stack on his turn and inflict huge losses (if you look at the gun fire of those times, I believe that huge losses of a hundred or so justified if we assume that these two moves are half an hour). To do this, you need to go through an open, well-exposed area, without any depressions, hills, buildings. You will not always find such suitable terrain (in my 40 battles, not counting games with bots, such attacks were undertaken only a couple of times), and in general ... Historically, such attacks were very rare, and always at the cost of huge losses, especially on a well-fortified position(Preussisch-Eylau). If you want to break through with stacks of columns (and this is the rule that works for the stacks, which you don't like so much) - select the best of the best soldiers, take losses, and take the position by storm the next turn. Otherwise, it will be necessary to hope that your poorly trained soldiers will not run away, which would be quite fair.
(However, again. If you look at the many maps of the main battles from different titles, it is very rare that you can't find a loophole or a convenient relief spot to have to attack head-on.)
Moreover, even when you have to fight in open terrain - it's not fatal for the full stack tactics!(which makes the effectiveness of artillery and soldier's fire even less significant) You just can move with spread out columns and unite only when you reach the enemy line. Or use line formations(it will take longer time but maybe somewhat less losses).

In most cases, you can attack by getting close enough. And attacking with an overflowing column just sweeps away the batteries. Yes, even at 50% there are huge losses, but you need to understand that in Napoleonic there is no way to repulse the guns. These batteries will be gone. And at points they are quite valuable.

After all, there is a counter battery battle, if you value the lives of your soldiers so much!

As for the infantry. I think that it's quite an important difference to kill 50 men(1\10 of 500-men-battalion) or 100(1/5). Maybe it will not cause great disorder, but at least defenders could ''sell'' the position at a higher price.
As a conclusion, I will say again - defence has ultimately to be more stable! I demand that! 

P.S. Don’t think that I'm judging reprehensible, but I have the feeling that you have not played enough controversial matches with expert players and didnt use different tactics against artillery positions (The Chosen One is a perfect proof of this. He is maybe the best player of NB I ever met).    

Nice writeup! Thanks!

Maybe I'm spoiled, as I come from playing the battle of Dennewitz (Leipzig 1813) multiplayer, where both sides have plenty of arty and the map does not offer alternatives to frontal attacks as the terrain is flat and feature-less. The best you can do is to use skirmishers screens, keep outside the fire arcs, and hide the "assault troops" behind "suicide troops" whose sole job is to block the LOS of the enemy batteries (and not to isorder the other troops once routed). I have to say that did not feel particularly immersive. 2 batteries of 12lbrs interdicted any kind of movement or deployment within 6-7 hexes within their line of fire, which strikes me as rather odd.  

Using lines to advance on artillery is not a real option (line movement disorder) -> disordered troops move slowlier and will suffer even more artillery fire.
Counter battery fire against deployed artillery takes ages (as it should, I suppose).

I will play some more on different maps, maybe the problem is very specific to my current Dennewitz game. :) It's true that the terrain in the battles of the second title I own (Bayonets on the Rhine) is much more restricted.