I'm trying to add texture to the layer with the bushes using an opacity mask, but the texture is cutting around the shapes on the layer that is below. I want to apply the mask to only the top layer with bushes. I've tried using the knockout group option but that doesn't seem to be doing anything. Can someone please help :(
The black portion of the mask is not solid black.
For an Opacity Mask you need to ensure the black on the mask is actually 100% black and the white is 100% white.
In RGB that means
R0/G0/B0 black and
R255/G255/B255 white, in CMYK that means
100C/100M/100Y/100K black and
If you do not have a solid black or white on the mask, then you get a "bleed through" opacity effect due to greys on the mask.
The reason you are seeing objects behind your mask is because that portion of the mask is a grey. Therefore, it partially hides the objects it is applied to.