Hey, I'm a runner and I've noticed an interesting phenomenon between flushes. There's usually a very distinct peak in my running pace, so much so, that I will either run a new Personal Best, or will come very close. Then it drops off. When I observed this about 10 yrs ago, the peak performance would occur 7-10 days after a flush and then would repaeat after the next flush. I recently started the same process this year in February, and I'm hitting new Personal Bests again, but this time the peaks are occurring 4-6 days after the flush.
When I did this 10 years ago, after a certain number of flushes the peaks kept getting wider and wider until I no longer had any "bad" runs. During that stretch I ran my very first Marathon and qualified for the Boston Marathon at an average of 7:30 minutes/mile. What I don't know is how many flushes it took to get to the point where I didn't have any "low points" between flushes.
I'm hoping to find that out this time around, but like you, I'm super-performing athletically in the first week after a flush and it's dropping off in the second week, and when it drops off, it really drops off, like 1 to 1-1/2 minutes per mile which is significant. I would try to flush weekly, but it's too damn inconvenient, so I'm going to stay with the two week cycle and see how it goes longer term.