There was a well-documented test conducted in the UK in 1942 where 16 Churchill tanks were driven through a 600x400 yeard area, pounded by 72 25-pdr guns firing at 72 RPM for 8 minutes while the tanks drove slowly through the area.
Just for the fun of it, I tried replicating that by parking 16 Churchill IIIs in such an area and pound them at roughly 84 RPM (24 guns each firing 7 rounds pr. 2 min. turn) for three turns. The catch is, that in the real test, they timed the shells for airburst whereas SP represents the shells gonig off on impact.
In the real test, many tanks were hit, one lost a track and another suffered damage to a bogie but managed to crawl out of the area.
The SP equivalent produced the following:
Game: tanks destroyed/immobilized
#1: 3/2
#2: 6/3
#3: 5/4
#4: 3/3
I did a fifth run, monitoring the hits
#5: 2/2
The two kills were by top hits, the two immobilizations were from "NON-PENETRATING" hits. There were plenty of both that did no damage. There was also a lot of side and front turret and hull hits which did no damage, but the PEN value of the 25-pdr hits on these locations could sometimes go as high as 5 (most are less though).
The 25-pdr has HE-Pen=2.
I replaced the Churchills with Crusader IIIs with lesser armour, particularily top armour which is 1 vs the Churchills 2
#6: 8/1 (one or two imobilized vehicles were later destroyed)
In this case, 6 were destroyed by top hits, one by side turret hit and one by a front hull hit.
Replacing the Crusader IIIs with open topped M10s resulted in carnage
#7: 11/3 (two of the immobilized vehicles were later destroyed)
All destroyed fell to top hits, which also caused most of the damage to the immobilized vehicles.
In the final test, I replaced the M10s with Staghounds with thin side and rear armour (1) but changed the top armour to 10 to prevent top penetrations.
#8: 5/3
In this case, all the destroyed vehicles fell to side turret and hull penetrations.
IF the number of vehicles destroyed or damaged by artillery fire is excessive - and I'm not saying it is - then there seem to be two culprits:
A: Too many top hits, as this is the real killer
B: The penetration value from HE is too high. In this test, a gun with a HE-pen value of 2 could end up anywhere between 0 and 5 and thus would be deadly to many armoured vehicles, particularily those with thin armour.
That's my take, anyway
Claus B