How are you giving these additional, more specific tests? I would think that your acceptance rates would start dropping once you get past five rounds or so.
My personal experience is that people new to interviewing are the ones who think that making individual interviews more precise will improve the process, but my experience is that improvements to the overall interview process aren’t done by improving how good individual interviews are.
You have between 10-16 hours of time with a candidate depending on the desire ability of your job. I like to break it into: 1 hour of pitch/expectation setting where the only screening is for ability to complete the process (language, appropriate background, etc) and to catch obviously fraudulent candidates, 4 hours of take home technical assessment (programming project), 4 hours of soft skill assessment (3 hours of prep and 1 hour of presentation is my favorite format) and 1 hour of meeting with the hiring manager.
But, the format is not really the point. The point is to have a specific thing you are trying to discern from your filter and to focus your efforts on making that the only thing you are judging on.
You have a budget for the number of hours you can make a candidate spend on work samples; it's the amount of time they'd spend in the interviews your tests are offsetting. This isn't complicated.
My personal experience is that people new to interviewing are the ones who think that making individual interviews more precise will improve the process, but my experience is that improvements to the overall interview process aren’t done by improving how good individual interviews are.