Value up top, position underneath. The MP opener's range still dominates most of what you would 3-bet thin.
The reference tier. 3-bets are linear and value-heavy, live-style; calls are pairs, strong suited hands, and the best broadways.
A middle open, you in the cutoff. The opener is wider than EP, so 3-bets earn more — but position still says flat the speculative hands.
Assumes a ~4bb open; 3-bet to ~3x the open in position, ~4x from the blinds — larger as stacks deepen.