There is no SOP to provide a feedback while you still have scheduled interviews. To me, you can ask for a soft feedback when you did well. I asked for a feedback after my 1st interview in the R2 with MBB. I felt I performed well and I basically said something on the lines:
"I feel one of the critical skills in consulting is the ability to quickly learn and adjust. My next interview is only tomorrow. Based on our conversation, do you have any suggestions for my next interview, in terms of the qualities I should continue to exhibit and areas I maybe should be more wary about (aka weaknesses)".
This way you are not asking for a direct response whether you've passed. You are mature enough to acknowledge that everyone has strengths and weaknesses and you are asking how can you improve further. However, based on the response, provided you get the response, you can deduce the feedback you are looking for, wether you've passed. In my case, the partner gave his feedback, very thoroughly, and I was able to use it during the next interview. I felt his feedback was useful and I passed the interviews.