Why ElasticSearch returns data only if query string more than 4 symbols?

Why ElasticSearch returns data only if query string is more than 4 symbols? Where I can to setting this? I use Elastica PHP client.
For example if I pass one symbol "O" in query I get empty result, if pass full word "Oleg" I get this. I tried to add filter for index: nGram, and set for it params: 1, 20, but without success

I can share my code