My homemade salad dressing is 2 parts oil to 1 part vinegar. So 2 Tbl of it would give you about 2 tsp of vinegar. Not a huge amount. So maybe the oil is buffering it for you?

1 Cup of oil
1/4 cup of balsamic vinegar
1/4 cup of red wine vinegar
1-2 cloves of garlic, diced or crushed
1 tsp of salt