Kano, a fellow tanker had the same problem, claimed he could hit a Panzer 4 10 times with a Panther and it wouldn't blow up. I reviewed the film closely..... Problem is in the film viewer, enemy tanks beyond 1k can't be seen on the film viewer, so I had to wait until he fired; rewind, track his turret to the nearest enemy tank, and watch each splash.
He was pretty much hitting all over the place; it looked like a HIT sprite on the center of the Panzer4, however its well known this is just because the Sprite is only one size; from an extreme distance it looks like the sprite is bigger then the enemy tank!
He was simply hitting all the soft spots on the tank; no real damage from it; hell at one point he puts a round through the window of an M3, it was a glancing blow; however from a distance it was a "kill shot".
I tracked about 15-20 shells, and just summed it up as "Bad aiming", he was accurate at 1.5k out, just wasn't accurate enough to hit the armor square up; it was always on an angle, or really bad shot.
Other times I tracked a Tiger 2 shot from 3.6k away and nailed someone at a spawn, from the film viewer my Shell landed about 20 feet BEHIND the tank; however his tank blew up and I was credited with the kill.... (wanted to save it for later but...doh)
Can't remember to many wacky things from flying, other then 109K getting magical hit sprites but the plane takes no damage (30mm shots only).