Re: What is the correct hand placement when do kote gaeshi?
Basically whatever you can pull off at the time. I would attempt all of them and see what you prefer. Early on in Yoseikan style we literally control hand while atemi, then break balance using arm (jujutsu style - leaning into the arm on turn). This would send Uke forward in the same direction of attack. The wrist reversal would then make uke slip or slide forward as his forward momentum is countered with a reversal movement taking out your feet sometimes in the process.
I have also studied Aikiki and appreciate the method of teaching the down and up and down movement with balance taking with Aiki. So, the corollory of that is I use it however I feel. If I make a big tenkan entry Aikiki style. If i slip the punch and strike, aikijujutsu.