I look directly at peoples mouths quite often, especially once I have become overstimulated by distractions in the room. It helps me to understand words, but it does nothing to understand expressions.
I also have a way to not focus my eyes. Kind of like when you notice something in peripheral vision, you can actually see it quite well, but without detail. If you want a closer look you turn and inspect for details of what you saw. I will sometimes washout the direct focus of where I am looking and try to see the whole picture instead of becoming bogged down with multiple details. This "not looking" allows me to "see" expressions much better, but it is something that I consciously have to do and I can see several levels of micro-expression.
I may not always know what they mean, but I can notice a contrast between rapid-fire expressions and it is enough to spot many liars who most people think are good at it. I know it sounds contradictory, but I can't really explain it any better. I get too much detail from looking too intently at someone's face, maybe. Looking at a stranger's face is like cleaning up vomit. You know you need to do it and you want to get it done quickly and not get any of it on you. Their emotions mirror strongly in me, sometimes and it can be uncomfortable to actually understand someone too much.
My son and I both seem to "Receive" others emotions if we look too closely and his reaction is to hide, but I have learned to not care or something.