Just playing a bit of devil's advocate here, but could it be the amount of gear people wear they simply don't feel/hear some hits? I run relatively light so I feel hits on my arms and legs easily, and a hit on my vest if it catches a mag is easy to hear - and a shot on the lid makes one hell of a sound so you can't miss it.
But I do wonder if people are wearing vest/pouches/hoodie - will they necessarily feel a shot over a longer distance?
I play by the rule of , "if in doubt - call a hit". I had one instance where I couldn't tell if I'd been hit on my leg - it was a soft tap, could've been a branch in the grass, or a loose strap - we were in the middle of an assault between a large open area so I called the hit.