When I learned a little bridge 26HCP's needed for 3nt unless you had reason to believe a 5 card or longer suit was useful. Also when I'm dealt 18-19 HCP's nt-ish, I plan on rebidding 2nt over pd's 1 level response. I can't know if pd will respond 1s or 1 nt. But my rebid will show 18-19 balanced. Pd can pass with bad 1s or bad 1nt response.