"Cis a is prefix that can be used when it's helpful to communication, to distinguish between a person assigned female at birth who identifies as female and a person who was assigned male at birth who identifies as female."
This assumes that
?our sex
?our sex role (gender)
?our internal gender ID (claimed as innate and most people have one but I've not seen anything to support this
Is an important part of our identity.
For the older ones among us, the whole language around "identity" is a bit new and unknown, hard to understand. I grew up in the days of "I am" "You are". So people would say "I am a girl, I am a goth. I am a big fan of Eastenders and I am not very interested in clothes". Or whatever. They would have their facts, and their personality, and it would be couched in terms of I am this or that, They are something else. I am a Goth, They are Casuals. Might be something you might hear said 
The first time I heard of "identify as" was around sexuality and it was about HIV and sexual health and not targeting things at "gay men" as some men who have sex with men did not "identify" as gay or bisexual and so they were left off / didn't consume the messaging >> instead we talked about "men who have sex with men" and that was clear.
Now it seems that "identify as" is more important than "am". And we are all assumed to have a core "set" of identiites that are fundamental to our being, one of them being sex. But, most people, espeically older ones I support, don't "identify as" a man or a woman etc. They are one. The identify thing is baffling and meaningless. And then you try to parse it by thinking about things that you might identify as. A christian. A sci fi fan. A model train enthusiast. I suppose it's about something that you are but that is also important to your self image, who you are? Many people don't feel this way about sex though. Or gender. It's just not an important thing. This is where it all falls down a bit. The assumption is that everyone has an internal gender ID and this is a core part of their "identity". Who have they asked? Trans people - by definition they have this. To extrapolate it to everyone else, is an overstep.
For many people the whole concept of "gender ID" as a core and internal part of their inner selves is simply, not. It doesn't make sense. So statements like "a person assigned female at birth who identifies as female" are baffling. Loads of women do not "identify" as female. People don't know what it means, they don't have this feeling, they can't conceptualise what this is.