Alright, so I'm in the process of removing those unnecessary add nodes and saturating the alphas. However, it turns out that what removed the black pixels in the opacity mask was setting the Opacity Mask Clip Value to 0.5 instead of 0.333. Currently I don't see a problem with changing this value.
this is quite sneaky - I like it. you don't need 2 lerps and an add at the end - just lerp between the two UV sets using your mask instead it's good practice to saturate the alpha input to the lerp because an outside 0:1 range value in the alpha could give unexpected results. it doesn't look like that's happening due to…