I have been having success using about .175 ml per pound grain bill, per .1 drop of pH, per total post boil volume. And if that amount might push the lactic flavor threshold I use phosphoric instead. For your beer I think you have room for more lactic.
.175 x 11.44 x 83% or about 1.6 ml
But its more about flavor, so I would try 1ml first. Then maybe add another if that doesn't do it.