[jp10]

From the description I think it is referencing the weaker side armor found on most MKIV models. Russian sources mention the same effects with 122mm HE. Rather than a Winsp style penetration, the armor plates were 'buckled' or 'bashed' by the explosive force, dislodging the running gear and breaking the welds in the lower hull.
Like the mentioned Stuka reference it had to be a direct hit on armor, not a near impact.
IDNK if there was a 'Quick' or 'Delay' setting involved. In my experience, HE Delay, generally was a 1/10th of a second and would allow a little more penetration before detonation. We used to drop HE Delay on entrenched targets to bury the round a bit before detonation to 'cave in' fighting positions rather than a ground burst with more shrapnel.