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.