With SD3 as you change the velocity of the note, it uses different sounds.
In this case, is it possible that when you use vel=100, it's using a sound that's
not right for you, but, since brushes are inherently a quiet sound, maybe using
a lower velocity, like 50 or 70 might access the correct sound that you're trying
to achieve.
Note: I haven't tried this, but computers are logical beasts and this seems logical
to me.