Why Apache2 total threadcount is more than MaxRequestWorkers

I recently moved my mpm from perfork to event (& also mod_php (php7.0) to php-fpm (proxy_fgi)) I estimated my max concurrent connection load to be around 300. So i set the following configuration in mpm_event.conf

StartServers                     5
MinSpareThreads          25
MaxSpareThreads          75
ThreadLimit                      64
ThreadsPerChild          35
MaxRequestWorkers         350
MaxConnectionsPerChild   0

Now I see some strange behavior when I observe the apache2 process and total threadcount using ps

Normally I have around 12-13 total apache2 processes (ps aux | grep apache2 | wc -l). Considering one to be parent.. so it is about 10-11 children. Further if I see the total threads count from apache2 with

ps -o nlwp $(pidof apache2) | tail -n +2 | awk '{ num_threads += $1 } END { print num_threads }'

I observe 408 threads for a long time.. So my questions are:

• how is it possible that total # of threads increasing beyond MaxRequestWorkers (350)
• how is it possible that total # of child processes increase beyond StartServers (5)
• What is the justification for 408? (12*34?) and is my traffic hitting a limit?

Thanks for your help in advance

I am observing similar behaviour. With default MaxRequestWorkers 150, I reach up to 301 threads - i.e. 1 parent and 2* MaxRequestWorkers threads.

I tested this by setting MaxRequestWorkers as 40 and I reached 81.

Can anyone confirm this Apache behavior?

P.S. I am running Apache2 as prefork, i.e. ThreadLimit and ThreadsPerChild are not used IMHO.