Now that I have had a chance to see what it is that you're trying to do, I see there is an easier way. I love clipping masks but sometimes they are not the best choice. Layer masks are not as editable, but in some cases (like this) it's not an issue.
I make this post so that anyone who may search this subject in the future will see options.
When removing the red background, we can see that this is a complete mess.
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Even on a neutral background, we can see that the "effect" is not contained.
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Here's how it looks just using simple layer masking.
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With a neutral background.
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Sometimes it's easier to keep things simple. Just my 2 cents.
You can use clipping masks with the "blend if" option. Works on all colors of rectangle shapes except white. More on that later.