The de facto Instant Pot manual at hippressurecooking has a page on cooking pasta but doesn't explain how to determine a proper amount of water to use when cooking pasta.
Figuring out the liquid is easy (no sputters) The hip method for pressure cooking pasta does not actually measure any of the cooking liquid. As noted in the recipe, only the amount of water that is needed for the amount of pasta to be cooked is used. This ensures that there is almost no liquid left in the cooker by the time the pasta is finished cooking – nothing left to foam or sputter when pressure is released.
There follows a recipe that instructs to "Pour in the pasta, the tomato puree, and just enough water to cover the pasta". 2 cups of tomato puree.
So not much help there. Presumably the amount of water that is needed for the amount of pasta to be cooked is related to the weight of the pasta rather than its volume—covering farfalle or rotini is going to require a lot more water per cup of pasta (but perhaps the same amount per gram) than is covering lasagne or spaghetti, because their shape makes these flat pastas more dense.
Is there a simple ratio of water to weight of pasta that will give consistent results with a variety of pasta shapes? If not, is there a chart somewhere that gives a water-to-pasta ratio for various shapes?