A combustor for a gas turbine engine comprising: a support shell (68;70); a first liner panel (72A;72B) mounted to the support shell (68;70), the first liner panel (72A;72B) including a first rail that extends from a cold side of the first liner panel (72A;72B), the first rail including a diffusion interface passage surface that is non-perpendicular to a hot side of the first liner panel (72A;72B); and a second liner panel (74A;74B) mounted to the support shell (68;70), the second liner panel (74A;74B) including a second rail that extends from a cold side of the second liner panel (74A;74B), the second rail being adjacent to the first rail to at least partially form a diffusion interface passage; wherein the diffusion interface passage defines a diffusion interface passage axis oriented at 30-90 degrees with respect to a hot side of the second liner panel (74A;74B); wherein the diffusion interface passage defines a pre-diffuser section, which is defined by a surface of the first rail and a surface of the second rail, and a diffuser section, which is defined by a surface of the first rail and a surface of the second rail, along the diffusion interface passage axis, and characterized in that the diffuser section at least partially defines an expanding passage where the surface of the first rail extends at an angle between 1-15 degrees with respect to the surface of the pre-diffuser of said first rail in an upstream direction and where the surface of the second rail extends at an angle between 1-15 degrees with respect to the surface of the pre-diffuser of said second rail 122b) in a downstream direction. a support shell (68;70); a first liner panel (72A;72B) mounted to the support shell (68;70), the first liner panel (72A;72B) including a first rail that extends from a cold side of the first liner panel (72A;72B), the first rail including a diffusion interface passage surface that is non-perpendicular to a hot side of the first liner panel (72A;72B); and a second liner panel (74A;74B) mounted to the support shell (68;70), the second liner panel (74A;74B) including a second rail that extends from a cold side of the second liner panel (74A;74B), the second rail being adjacent to the first rail to at least partially form a diffusion interface passage; wherein the diffusion interface passage defines a diffusion interface passage axis oriented at 30-90 degrees with respect to a hot side of the second liner panel (74A;74B); wherein the diffusion interface passage defines a pre-diffuser section, which is defined by a surface of the first rail and a surface of the second rail, and a diffuser section, which is defined by a surface of the first rail and a surface of the second rail, along the diffusion interface passage axis, and characterized in that the diffuser section at least partially defines an expanding passage where the surface of the first rail extends at an angle between 1-15 degrees with respect to the surface of the pre-diffuser of said first rail in an upstream direction and where the surface of the second rail extends at an angle between 1-15 degrees with respect to the surface of the pre-diffuser of said second rail 122b) in a downstream direction.