why ajp idle threads are not increasing?

apache server ->(ajp, 9009 port) tomcat server

on tomcat sever.xml, I set minSpareThreads ="100", maxThreads = "512"

1. but when tomcat restart threads starts at 1 not 100 (netstat -an |grep 9009 |wc -l)

2. also no matter how many http request, ajp threads do not increase (they only increase until 19-20)

3. I got other tomcat server almost same configureation(server.xml) it increase until 100 without minSpareThread, maxThreads options

in this case what other options I could look at ?