i figured it out, you have to for the b21xxEXbf1 b21xxdb3 33xxbf1 combo they wont drop out if instead of the second b21 you just do b2xxdb3 instead of the b21xxdb3 and this reduces the combo damage by less than 1 percent.
full new combo
b21xxEXbf1 b2xxdb3 33xxbf1