I've been playing D-Day - The Great Crusade off and on for several years now. Granted, I have soloed entirely. I have learned that understanding the use of artillery is the key to success for either side. Therein lies my problem. The rules do not give me a firm grasp on whether or not TECs modify columns on the Artillery Table. Combat resolution very clearly says to adjust the combat table either left or right for TEC effects (plus other variables not in question). Bombardment Resolution (13.4) describes under "Procedure" item (c) "Apply any column shifts;" Whether these column shifts apply to TEC or Disruptions is not clear. Is it one or the other or both?
In my experience, this one impact (and I've played it both ways) has a huge impact on the outcome.