The whole idea behind a CIRAS is that it's pretty adjustable. A "medium CIRAS" can fit a small person or a large person, depending on how you set it up.
I don't know what you consider "really small", but I'm about 5'6" (on a good day! :P) and 190lbs (32 inch waist) and I have a "medium" Phantom CIRAS which fits me perfectly. I could also fit someone much smaller.
If this CIRAS is "large" it might be too big for you. If it's "medium" it will be fine!
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