I like to play this as 18-19 HCP. With most of my partners we play transfers are on after the 2NT response which allows Responder to describe their hand shape or strength of a major raise: 3♣ Transfer to ♦, Responder may pass with ♦, no ♠ fit, and a weak hand.3♦ Transfer to ♥, Responder may pass with ♥, no ♠ fit, and a weak hand.3♥ Transfer to ♠, stronger ♠ raise.3♠ Weak ♠ raise. This is described in detail in Max Hardy's book "Advanced Bridge Bidding in the 21st Century.