Very good question. This is something I have never looked at and thus I set up a test scenario and the results are:
1. When firing thru a skirmisher hex the units in an adjacent (or further back) got a -20% benefit.
2. When the skirmisher was on TOP of the stack with the formed infantry unit there was NO benefit.
Thus in answer to you question: No, they do not.
If you want protection from skirmishers you must put them out at least one hex from your formed units/guns. And of course fire on skirmishers is reduced as well. Thus firing at skirmishers thru another hex of skirmishers would also incur the bonus for the light infantry screening the hexes behind them.
Good question and perhaps a few of us didnt know this one ...
Chef d'Escadron Bill Peters
Armee du Rhin - V Corps, Cavalerie du V Corps, 20ème légère Brigade de Cavalerie, 13ème Hussar Regiment
HPS Napoleonic Scenario Designer (Eckmuhl, Wagram, Jena-Auerstaedt and ... more to come)
[url="http://www.fireandmelee.net"]Fire and Melee Wargame site[/url]
