Okay, you are printing very large and tests/mistakes eat up a lot of chemistry, paper and time . . .me, in fresh chemistry I would bleach and sepia tone a decent sized test strip containing some highlights and have that on the side for comparison.
I am not clear on your dilution, but I like a stronger warmer mix so I can clearly see the toning progress in rapid fashion. It should be quite obvious when toning is complete. Much harder to tell when it progresses slowly.
In any event, I never fix after sepia because all the silver has been converted. Again, it would be sound chemistry to do so, but that assumes your toning is not complete. That is the real problem, unless you are doing stuff like sepia splits.