I'd like to answer a question you didn't ask. Personally speaking, I play best when everything is RELAXED. I notice something in you that you see often in pool halls. Your face is all scrunched up. Lips are tight, forehead furrowed. Maybe your glasses are causing that. I find it hard to keep one part of my body relaxed when another part is tense. If your face has tension it is likely the muscles related to delivering the cue are also tense, even just a little. Again, for me personally, when I learned how to deliver the cue while maintaining relaxation, questions of head position or feet or all that stuff just didn't matter. Balls go in from everywhere as long as your muscles allow you to deliver the due in the direction you want it to go.
Great point. Studies have shown that facial expressions can alter the mindset, affecting how the mind perceives your current situation. A frown or angry expression tells the brain to tense up the muscles and get ready for conflict. A smile tells the brain that all is good, no stress or bad shit is going down. In other words, when Efren laughs off a mistake or error, he is keeping his mind calm and collected, which keeps his stroke mechanics smooth and free of unnecessary tension.