Gulenko says about ESI-fi: 'Subtle, sensitive nature, is a good judge of character and a reliable friend, is capable of compromise. In their softness and ease of contact he sometimes resembles an SEI ethical subtype.'
Socionics Types: ESI-ISFj Subtypes (sociotype.com)
And the reason this stood out to me was that my first crush was on an ESI boy (likely fi subtype). And most recently I fell for an SEI-fe boy, and I did see some resemblance.
Personally I think ESI and SEI are the most magnetic types, I think S types existed before N types, and SEI and ESI were the original sweethearts of the sociotype