When exporting the config, only lastSuccess shows.
jenkins:
unclassified:
perforce:
lastSuccess: false
 

Defining other globals opts, like  "headLimit: 100" gives error:

12:28:19  io.jenkins.plugins.casc.ConfiguratorException: Invalid configuration elements for type class org.jenkinsci.plugins.p4.PerforceScm$DescriptorImpl : headLimit.

12:28:19  Available attributes : lastSuccess

{{}}

Immediate need is maxFiles, maxChanges, and headLimit{}