3 pieces.
Only one position exists at this depth.
4k3/8/8/8/8/8/2R5/1K6 w - - 0 1
pure model ideal mirror single-piece single-piece:black nocapture nocheck
Published as Ban (1965)
Deepest dual with different first and last moves: h#4.5. The deepest dual overall is h#5, where the two solutions share a first or a last move.
Only 2 distinct ideas exist at this depth.
4k3/2R5/8/8/8/8/8/2K5 w - - 0 1
Two solutions, with different first and last moves (2 starts, 2 ends).
pure model ideal mirror single-piece single-piece:black nocapture
4k3/3R4/8/8/8/8/8/2K5 w - - 0 1
Two solutions, with different first and last moves (2 starts, 2 ends).
pure model ideal mirror single-piece single-piece:black nocapture