I think that you could be right about it being designed for a Chinese person. A bike cape, like so much in life is a compromise. I have actually given some thought to designing and making my own. Just up the street from me is a factory that makes marquees, lorry covers and suchlike, and I could probably buy offcuts for next to nothing.
The advantage would be that I can tailor it to fit my bike and my person, and make the straps to the size and position that suits me. I favour a heavier fabric, as it is less likely to blow about in the wind. Another idea would be curtain weight at the lower hem.
A car is no longer an option for me due to eyesight issues. If I really want to stay warm and dry, there is always my favourite armchair by the fire with my slippers and [vape] pipe, but I am not ready for that yet, or at least not full time!
On the plus side, I reckon that here in Lincolnshire, I probably ride in rain less than 12 days a year. Now I have bought a new cape, it will probably stay dry for a month. If I could guarantee it, I would buy a new cape every month.