A few things on vinaigrettes and emulsifications...1:3 vinegar is the traditional ratio, more oil will break it. Less oil may make it too strong. Substituting water can help to get the consistency you want. Grainy Dijon is delicious addition, but doesn't work as an emulsifier. You'll need at least a small amount of regular Dijon to keep it from separating. Honey and Dijon are the two emulsifiers I use, but not always both. My favorite additions are a small amount of shallots and herbes de Provence (dried Rosemary, thyme, lavender, marjoram).
For a great, simple mustard vinaigrette
1/4 c. White wine vinegar
1t Dijon
1t grained Dijon
1c olive oil (I like pure olive oil, it doesn't take over flavors like virgin)
S+P
add water until the consistency is right for what you want (for this amount, about a tablespoon should work)