ETA: Oh - one other consideration with the headwings... FF'ing, when you have the harness straps at the next slot above your DC's shoulders, the headrest is supposed to come down to be just above the shoulders....so that it is pushing down the harness straps. This bothers me, personally, I don't like the idea of the force of the kid in a FF'ing accident, pulling the harness straps that are under the headwings and potentially pulling the headwings out at an angle from the seat for him to crash back into.
And if the headwings don't pull out, then they are clearly interfering w/ the harness straps, which is always put out as something not to do. There doesn't seem to be any clear evidence of how this really works out in a real life crash, not that I've seen anyway...and I'm probably overthinking it... but something to be aware of. I think most (all?) other seats w/ SIP headwings have harnesses that adjust w/ the headwings. (I think). I've made the decision to put the headwings above the next harness slot when we have it FF'ing...against man. directions...but it feels safer to me. In our case right now, that puts the bottom of the wings right about even w/ the bottom of DS's ears, so his head is still pretty well protected I believe.
(*not a tech, and I've seen nothing to back that thought up.... just a mom who loves her little boy, owns one of these seats....and way overthinks all the "what if's")