When firing HE rounds with the 40mm UGL the rounds are not exploding where they should.

Observations -

When I fire at the 100m targets I can see the HE round land at or near the targets feet but it seldom, if ever, explodes there. There's a short delay of about 0.5-1.0 second from when I see the actual round hit the target to when the explosion happens about 50m or so behind the target. But I've also seen explosions about 100m behind the the target when the actual round was dropped at the targets feet, the round can also instantly explode about 25-50m in front of the target. Sometimes the round doesn't even explode.
When firing smoke at the 100m targets though, the round goes where it's supposed to and ignites close to the targets feet, as expected.