I didn't find koshi defined the way you do in the literature I consulted. Did you receive that teaching from someone else or did you create that definition ?
First about me. Yes I was taught weight underside and Koshi many years ago as standard procedure. Since coming to Aikiweb and assuming everyone knew about it I find that not many do apparently.
I wasn't taught by academics and looking it up and finding it's history and debating the pro's and cons etc. so when I see others debating things or I know something then I know that if I now search I will find some reference somewhere to it. So my research is more to do with validating what I already know and do. So yes it is my definition but I can find and give references to it from sources on the net. I found a great one recently.
I'll look it up again and post it.