Obtaining epic information from issue REST API

I’m receiving issue information from /rest/api/2/issue/{issueIdOrKey} and getting epic information through com.pyxis.greenhopper.jira:gh-epic-label custom field (epic id -> epic name).
One of the customers configured his instance in a way epic queried by REST contains two com.pyxis.greenhopper.jira:gh-epic-label fields actually represent related issues (?).
This is obviously an edge case and not a problem per se, but maybe there is a better way to find out epic name from issue from the one listed above?
p.s. I am aware about /rest/agile/1.0/issue/{issueIdOrKey} endpoint, but can’t afford sending two queries for every issue (we process thousands of them every time).