Gary,
I think your 'net -2' for enfiladed skirmishers is not a bad idea. You may be interested to know that Jonthan Leach related in 'Rough Sketches' that once la Haye Sainte was taken by the French, the position of the 95th's companies in the sandpit became untenable due to a withering 'flanking fire' and they were forced to withdraw back up to the main ridge position. So I think it definitely the case that skirmishers could be taken by enfilade fire in this way.
As for the 6 needed to bring on French cuirassiers at Essling, I recall the score was even tougher when we originally fought the scenario !
regards
EC