since cuts of meat and cooking vessel shapes and (tight) fitting lids are all different, i go by the rule that in a braise such as a pot roast, the liquid added should only come up to about 1/3rd of the side of the meat, no more. the meat itself will lose juices, as well as the accompanying veggies, so i usually even start out lower than that; around 1/4. often, when finished cooking, the liquid level will almost be up to 1/2, so judge it on the low side.
The way that you wander is the way that you choose. The day that you tarry is the day that you lose.
Sunshine or thunder, a man will always wonder where the fair wind blows.