Yeah, it's actually quite a subtle thing going on with the pelvic tilt. A less crude and perhaps more instructive verbal communication might be "Imagine you are going to sit down in a chair without looking behind you or using your hands. Your feet are shoulder width apart. Start that movement, then stop because the chair got moved away." Usually that stops the shoulders back thing (because now you would fall backwards) and brings them more forward, gets the pelvic tilt right (as opposed to just sticking the butt out), and the small squat. Plus, most people have had the experience of sitting in chairs, so it is familiar. For many, a connection to the familiar is comforting when trying something new and scary!