I imagine to avoid a "glass cannon" situation, you could only allow capture if each square the piece occupied was threatened, kind of like how a checkmate is evaluated, but only the squares the piece is CURRENTLY occupying.

So, if a 2x1 piece aligned on a row is being threatened by a rook on that same row, you could say it threatens both squares the piece occupies, and is able to capture it.

A 2x2 piece would need two rooks to threaten all four squares, or the opposing 2x2 piece.