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 (124a'; 124a") that extends from a cold side of the first liner panel (72A;72B), the first rail (124a'; 124a") 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 (124a'; 124a") to at least partially form a diffusion interface passage , wherein: the first rail is trapezoidal shaped, wherein the trapezoidal shape and the second rail define a pre-diffuser section of the diffusion passage and a diffuser section of the diffusion passage , or the first rail (124a") is ramp shaped and the second rail includes a ramped end section , wherein the ramp shape and the ramp end section define a pre-diffuser section of the diffusion passage and a diffuser section of the diffusion passage , characterized in that the diffuser section defines an expanding passage that extends at an angle between 1-15 degrees with respect to a surface that forms the pre-diffuser section . 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 (124a'; 124a") that extends from a cold side of the first liner panel (72A;72B), the first rail (124a'; 124a") 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 (124a'; 124a") to at least partially form a diffusion interface passage , wherein: the first rail is trapezoidal shaped, wherein the trapezoidal shape and the second rail define a pre-diffuser section of the diffusion passage and a diffuser section of the diffusion passage , or the first rail (124a") is ramp shaped and the second rail includes a ramped end section , wherein the ramp shape and the ramp end section define a pre-diffuser section of the diffusion passage and a diffuser section of the diffusion passage , characterized in that the diffuser section defines an expanding passage that extends at an angle between 1-15 degrees with respect to a surface that forms the pre-diffuser section . the first rail is trapezoidal shaped, wherein the trapezoidal shape and the second rail define a pre-diffuser section of the diffusion passage and a diffuser section of the diffusion passage , or the first rail (124a") is ramp shaped and the second rail includes a ramped end section , wherein the ramp shape and the ramp end section define a pre-diffuser section of the diffusion passage and a diffuser section of the diffusion passage , characterized in that the diffuser section defines an expanding passage that extends at an angle between 1-15 degrees with respect to a surface that forms the pre-diffuser section . <EOS>