Great patience and ingenuity to conduct such a test but I disagree with your findings at least in the case of garlic.
I think that there might be a difference btwn yogurt unable to form and garlic actually killing off the good bacteria.
I fermented cabbage with organic raw garlic and the resultant sauerkraut turned out just fine. The garlic in no way that I could discern inhibit the good bacteria from doing its thing,fermentation. However, for the record, I eliminated garlic this yr just in case of any interference although i will continue to eat plenty of raw garlic by itself.
I agree with James that it is safer to get caprylic acid from coc oil.