This flat metal sieve that came with the pressure cooker for

I use a pressure cooker quite often and its all about the cut of the meat. Much like slow cooking, using a often cheaper, fatty cut with lots of connective tissue - a chuck roast for example, yields much, much better results. Lean cuts of meat are make for fast searing and that's about it. If you try to coax them to be fall apart fork tender, you'll fail - those are the cheap, fatty cuts that go that way.

There is no rule, you should use the cooking times in your chart or a reputable timing chart, I use this one hippressurecooking.com/pressure-cooking-times

Basically, you'll want to phase-in the ingredients. That means, cook the beef roast for the time your cooking chart says, say 30 minutes, then open the pressure cooker and add the vegetables and pressure cooker them for their cooking time 4 minutes.

BTW, that same blog has a section where you can post a recipe and they will convert it to the pressure cooker for you. That's here: hippressurecooking.com/recipe-conversions