Any test which involves reagents that either directly or indirectly neutralize chlorine would be affected by a high FC.

The Taylor pH reagent has chlorine neutralizer in it. The amount of neutralizer is based on an FC concentration of 10 ppm or less which produces the accuracy the pH is designed for.

When you test for TA the first reagent you add is the neutralizer. Again, the test is designed to check a particular operational range of alkalinity at "normal" FC levels, that is, not at shock concentrations.

The Taylor site has some good articles, not easy to find unless you drill down a few layers. This paper discusses Five Sources of Error in Water Testing. All of them are interesting; #5 answers your question.