Prevent NUnit from executing test setup method from another class?

Question

I've got an odd question for which Google has proven barren:

I've got a project in .net with ~20 classes that all have tests in them. One of the classes has common test setup code, although a few of the classes have their own TestFixtureSetup that looks exactly like the common class (not my architecture choice - this predates my employment). I have my own test class for which I have some different code that runs prior to running a few particular tests within the class.

Some more info that's relevant: The custom setup code that I have enables data to be available for a few combinatorial tests I have in my own test class. As the value source for the combinatorial params, the List that is returned first initializes some data.

Alright, here's the question: When I try to run a test in ANOTHER test class, it's "building" the tests from every other class. In my case, it's building the combinatorial test that I have - and thus, triggering the custom setup method that I have.

How do I prevent NUnit from building tests in other classes? As in, I run a test in one class, all I'd like NUnit to do is build tests from that class ONLY.

I tried to remove any NDA-no-no language, but here's the combinatorial I have:

[Test, Combinatorial, Category("Regressive")]
        public void Test05_CombiTestExample(
            [ValueSource("ListA")] User user,
            [ValueSource("ListB")] KeyValuePair<string, string> searchKvp,
            [ValueSource("ListC")] string scope)
        {

And here's one of the lists that is being reference:

public IEnumerable<KeyValuePair<string, string>> ListB
        {
            get
            {
                InitCustomData();
                if ([Redacted] != null)
                {
                    return new Dictionary<string, string>()
                        {
                            [Redacted]
                        };
                }
                return null;
            }
        }

The line in question is "InitCustomData();" which, because my combinatorial is being built prior to running any setup or anything, is being executed anyway. I want this to stay here - I just don't want NUnit to start building test cases from any other class besides the one it's currently running a test in.