I think Duncan said it correctly and succinctly.
I found this on the internet and surprisingly I may have also attended the lecture at a different event.
http://etloh.8m.com/strategy/artil.html
I did not take notes but the author of the site did.
By James Sulzen
Excerpt:
British Artillery Practices
The British had a very different system. They gave their people (artillery and FOs) good maps with grids marked on them. The artillery would plot its own grid coordinates when it set up. To request a fire mission, the FOs would call in the grid coordinates of the target to the artillery. Then to calculate firing distance and angle, the artillery simply assumed that the earth is a perfectly flat, infinite plane (take it from me, it ain't) and did the standard (7th grade?) calculation:
distance = SQRT( (x1 - x0) ^ 2 + (y1 - y0) ^ 2)
and similarly for the angle calculations (SOHCAHTOA if I remember the mnemonic for the Law of Cosines from high school trigonometry).
The British could then fire spotting rounds and correct just like the Germans, but this would have required sticky arithmetic calculations, even if only linear interpolations. Also there's the time delay to work all those formulas out. So instead, the British just accepted the errors and tended to fire every available battery at the target. Since each battery's fire would tend to be somewhat in error relative to the other batteries, this had the useful effect of blanketing a large area around the target, as well as the target itself. (And probably any Tommy close enough to observe the target.)
The British were ignoring a whole host of errors that the Germans carefully accounted for (elevation changes, wind, temperature, etc.). By using many batteries, they could get a large enough area covered so that they would have a reasonable effect on the target. Also, they got their impromptu fires really quickly: Something like two minutes from the time of the first call until those shells are bursting everywhere.
There are a few major drawbacks to the above system. While fast it is not accurate, wastes a lot of ammo, and ties up a lot of division artillery assets. Also, it requires accurate maps with many terrain features accurately located on the map (i.e., cross roads, stream beds, towns boundaries, etc.). The British tended to assign fairly senior NCOs and experienced personnel in the FO role so that they wound up mitigating the problem somewhat of wasting ammo (i.e., the more experienced FOs had good judgment as to what was and wasn't a worthwhile target). Also, it seems that only FOs called in missions (at least that is my impression).
I presume (but have no specific references) that the British could have and did use the German system of setting up registered fire when they had occasion in more static situations. Also I should mention my reservation that I have a hard time believing the allegation that the British habitually fired an entire division's worth of guns (more or less) for each fire mission.
On the site the author also describes German and US artillery.
This may not explain fully the rationale behind the CS artillery figures but it does explain that the guns were not expected to have every shell hit the target precisely, during indirect fire missions.
When I have a moment I will explore the web for more info.
As the distances increased the impact field was spread further so that the effect of concentrated fire was not as concentrated?
Or, the original Talonsoft team took a guess?
But, I doubt they did.
HSL