Something that may be the cause if your fail-to-hit issues is this I almost remember.

If an entity is both small and fast enough, it can potentially pass its entire mesh/bbox
all the way through the surface of the "hit" models mesh/bbox.
That is, the bullet is now completely "inside" its target, not touching any sides.
If this happens, an event wont be triggered.

I cant remember the fix, but ONE had something to to with a c_trace backwards at
the start of the bullets frame. But Im not sure.

It was discussed at length, with multiple work-arounds suggested, by a few different
threads on this (gamestudio) forum.

I suggest you do a forum search on "bullet" and "too fast"

Best of luck.

PS : Maybe before searching, to test if this IS the problem, try clamping your bullets
slower with phent_setmaxspeed.

PPS : Not sure if its applicable unless the target is a registerd physics object too,
but check the manual for "ph_check_distance". It MAY be of help.