Brucemuir, there is a big difference between your tank processing and Jobo rotary processing. There is a lot of air involved in Jobo rotary processing which can potentially cause the developer to oxidize significantly due to constant rotation of the drum and cause a significant loss of its developing capacity. However, some people have claimed that they followed Jobo's chemical volume guide, which suggests even less developer for a roll of 220, and got good result still. I seem to be the only one who have experienced the opposite that I have had many processing failures by using 730 ml or less developer for a roll of 220 on my ATL-2300.
Hrst, I will shoot a roll of 400VC 220 as soon as I can and use 500 ml of fresh chemicals to process it in my ATL-2300 again. I will report the result here when it's done. I already know that if I process it with 850 ml the result is excellent. Now I will test it with 500 ml (470 ml actually because ATL-2300 can not be set to 500 ml. 470 ml is the closest). I hope this will help in revealing the fact about the C-41 developer capacity question that seem never gets a real answer so far.