New potatoes in pressure cooker with salt: how to optimize water amount and cooking time?

I am trying to replicate a recipe that my father-in-law performed once at home… well, not much of a recipe, rather a cooking style, as you'll see.

The idea is to cook new potatoes (specifically, new Ratte potatoes) in a pressure cooker with salt. The potatoes are easy to find (at least here in France), and are quite small: about 5 cm in length. After scrubbing them but leaving the skin on, he put them at the bottom of the pressure cooker, with a little water and quite a bit of sea salt. After a small cooking time (which I estimated at 5 minutes), the potatoes were cooked just enough and crusted with salt.

Now, I have tried that three times myself, and the results were disheartening. The first time, I had put too little water, and burnt the bottom of the potatoes. The second time, there was too much water, and I ended up with regular pressure-cooked potatoes floating in salty water. The third time, I overcooked and while there was no excess of water, half the potatoes has exploded into mashed potatoes (and there was too much salt).

How could I get an idea of how much water, salt and cooking time is needed for this recipe? Trial-and-error is not working very much here, and I have no idea how to figure out these quantities.

PS: it's not relevant to the question, but he made with that an olive oil/coriander/chili sauce that was real good. That I managed to reproduce, at least!