Simple Ad Hoc commands results in many UNREACHABLE hosts

I have about 200 servers in my hosts file. I can ssh to those servers without entering a password. ssh and no errors or trouble. When i attempt to run a simple Ad Hoc uptime command more that 50% of the servers show up as UNREACHABLE. Are there any setting I can use to improve this? Salt uses --async to improve response rates. Does ansible have any command line flags that are similar?

[privilege_escalation]
become=True
become_method=sudo
become_user=root
gathering = explicit
[inventory]

[ssh_connection]
pipelining = True

There is an async, but that should not help with unreachable, it would
help to know WHY they are unreachable, normally running with -vvv
gives you helpful information on what is happening at the connection
level.