How is the Splunk Heavy Forwarder used to buffer/cache until indexers come back online after getting disconnected?

All, I have a Splunk heavy forwarder collecting data from various endpoints, which then passes up to the Indexers. We recently had a config error that disconnected the HF from the IDX for a few hours. Some data was lost, some was not. We have PLENTY of disk space on Heavy Forwarders and our understanding was the HF would buffer/cache until the indexers came online. This does not seem to be true. Or was there a setting I simply missed? thanks in advance, -Daniel