Based on your comment describing the problem you're trying to solve: "The idea is to make the elements that fall outside a range transparent. That's why there is OR. Bigger than a certain value, smaller than a certain value. You can pick any number. 4 and 6 are arbitrary." I think you've overcomplicated the problem. If all you want is a vector of true or false values depending on whether or not the values in x are in your range you need neither ismembertol nor find.
justRight = ~tooSmall & ~tooLarge;
Let's look at the results as a table.
t = table(x, tooSmall, tooLarge, justRight)
If we were to use justRight to index into x, we'd get two elements.
If we were to use tooSmall and tooLarge to index into x, we could get the other eight elements.