The 3-bet does the defending; the short call list is pairs and premium suited hands only.
The reference tier. 3-bets are linear and value-heavy, live-style; calls are pairs, strong suited hands, and the best broadways.
Small blind against a cutoff steal: mostly 3-bet or fold. Flatting builds multiway pots you play blind-first for the rest of the hand.
Assumes a ~4bb open; 3-bet to ~3x the open in position, ~4x from the blinds — larger as stacks deepen.