It is about the same, you can also change
"Max connections", "PHP_LSAPI_CHILDREN", to 10 and 100, see which one does better.
PHP_LSAPI_MAX_REQUESTS can be increased to a larger number.
How many total requests served for each run? I think it should be >1000.
There is likely some factor affect the consecutive run of the benchmark tests, there should not be huge differences between them. Maybe the time you wait between each run has impact on this as kernel takes some time to recover from massive amount of sockets created from previous run?
I may try to reproduce this in our lab to figure out why if I get a chance.