If "Start Offset" is set to 0, and "Start Offset Attack" is set to 5 MS (it's the per default the lowest value)
you will get a 5 MS fade in on the attack when the "Start" controller on the perform page ist set to 127.
Usually only audible with instruments with a super fast original attack like snares.
Check also if you test a patch which offers maybe multiple variations of the same note. You can be easely be fooled if you listen to two different samples and riding the "Start" controller. The best way to check these kind of settings is to switch off all available repetitions except one, switching off the red circles above the humanize area.
best
Herb