Medium is where Shikaku grows teeth. Every board in this tier requires at least one common-cell deduction: a clue whose candidate rectangles all overlap on certain cells, which quietly claims those cells and forces a neighbor's hand. Singles alone won't finish these.
Clues sit mid-rectangle more often, areas run larger, and you'll hold two or three open possibilities in your head at once. The payoff is the click when a contested region resolves — the signature Shikaku moment this tier is tuned to deliver.
The 7 × 7 and 10 × 10 sizes are the sweet spot for medium boards; graduate to the hard tier when they stop stalling you.