I actually go the other way on that. When extended, the UA F headrests are perfectly comfortable, but when lowered they are far too low, plus they stick out from the seat quite a bit and thus very uncomfortably dig into my back (I'm 6'2"). Combined with the silly rule that the headrests must be lowered for taxi, takeoff and landing (no such rule on CO), this makes for fairly long annoying periods where I find myself wishing I was on CO.