As of now I don't need it for my own (I still run dovecot 2.3 on my server) and I don't have the issue with the default settings for dovecot 2.4 on servers of mine customers, so you might learn the documentation on your own here: https://doc.dovecot.org/main/core/plugins/fts_flatcurve.html
Probably somebody else can share their optimized configs.