Mateface gap configuration for gas turbine engine

In a gas turbine engine, adjoining pairs of airfoil structures include airfoils mounted to respective platforms. The platforms have side edges defining matefaces that form a mateface gap extending from an upstream edge of the platforms to a downstream edge of the platforms. A flow field of working gas adjacent to endwalls of the platform comprises streamlines extending generally transverse to the axial direction from a first airfoil toward an adjacent second airfoil. To achieve improved aerodynamic performance, the mateface gap has portions oriented transverse to the streamlines and oriented aligned with the streamlines. A step in elevation of the side edges at the transverse portion can include injected cooling flow in a direction that enhances attachment of the flow at a downstream side.