I have looked at your sizing chart and you have a very comprehensive list–with the exception of my bird–the Cape or brown-necked parrot. I have measured her at the girth which is approx 8″ and the nape to tail at 5″. I’ve tried using a model that I no longer see listed as these were for a CAG I had but they are listed at size 8 and are too large for my cape. So she is smaller bodied than a CAG, but definitely larger than say a Conure or Hahns Macaw I’ve also owned, so can confidently say this.
The body type is stockier like an African Grey, but smaller I think so perhaps a wide or wide plus would fit her. I hope the measurements clear that up — and then you can add the Capes to the list too! I have used these for years and love them–can’t say the birds do, but I find the younger they are, the better. It’s the rescues that are the least likely to accept them.
Based on the measurements provided, the size Wide will probably work the best.