I'm stuck waiting for the cat to come back inside, so while I don't have the brainpower to look at how grenades work now and answer the question "what should this be called", I do have it in me to look at the two preexisting names and say what they should be.
Impact: launch a grenade that explodes exactly when it might otherwise bounce.
Airburst: launch a grenade that explodes, modulo accuracy concerns, at the location (including elevation) it was targeted at.
Now, that definition of "airburst" leaves undefined the case in which the grenade hits something before reaching its post-accuracy-adjustment target. Having the round fail to detonate is almost certainly not what the player would want in the vast majority of circumstances, so that leaves either detonating or bouncing on premature impact. I think detonating would be the superior choice, what with being more player-friendly (if they wanted to bounce, they could have used timed mode), but either would be defensible.
With the caveat again that my brain is mostly not working right now, the current mechanic feels closer to airburst—but I do note that when elevation is changed before firing, the shot travels significantly beyond the target point before detonating.
So yeah, more after sleep.
~J