Change Mask's opacity in Compositor? I'd like to change the opacity of this ink bleed that i've made using a couple of masks. 
Here's my node setup: 

I've tried adding a mix node and a set alpha node and attempted at changing the fac. value in hope of changing the opacity but it's not having an effect so i was hoping someone could help me out,

cheers for any help- much appreciated!
adjusting the value of a mask is accomplished by adding a math node in multiply mode. The second value acts as a multiplier for the alpha.

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