Splunk & Log4j2: How to get pattern to work

I am using log4j2 to log directly to Splunk.

Earlier, I used log4j2 to log to a file instead.
I was able to get output like the following.

2019-03-06 18:44:47,757 INFO  [example.ServiceFileStore] WcmServiceFileStore [/vagrant/source/application/vagrant/source/application/webscripts] with [160] documents

When I did that the pattern for the file-based logging was the following.

<PatternLayout>
  <Pattern>%d %-5p [%c] %m%n</Pattern>
</PatternLayout>

---

When I try to log to Splunk directly I get the following result.

{"severity":"INFO","message":"WcmServiceFileStore [\/vagrant\/source\/application\/vagrant\/source\/application\/webscripts] with [160] documents"}

The time is not needed in the pattern, but the logger, [%c], would sure be nice to have.

Is there a way to configure this for the Splunk Logger (version 1.7.1)? The configuration I am using looks something very similar to this.

<Http name="SPLUNK_QA">
  <Source>legacy_webapp.qa</Source>
  <SourceType>log4j</SourceType>
  <Url>https://mysplunkcloud.com</Url>
  <Token>*******-****-****-****-******</Token>
  <DisableCertificateValidation>true</DisableCertificateValidation>
  <PatternLayout>
    <Pattern>%d %-5p [%c] %m%n</Pattern>
  </PatternLayout>
</Http>