diff --git a/source/engines/iw_engine/formulas.cpp b/source/engines/iw_engine/formulas.cpp
index e7ab4b8..4a24d0b 100644
--- a/source/engines/iw_engine/formulas.cpp
+++ b/source/engines/iw_engine/formulas.cpp
@@ -38,25 +38,24 @@ namespace omath::iw_engine
     Mat4X4 calc_perspective_projection_matrix(const float field_of_view, const float aspect_ratio, const float near,
                                               const float far, const NDCDepthRange ndc_depth_range) noexcept
     {
-        // NOTE: Need magic number to fix fov calculation, since IW engine inherit Quake proj matrix calculation
-        constexpr auto k_multiply_factor = 0.75f;
-
-        const float fov_half_tan = std::tan(angles::degrees_to_radians(field_of_view) / 2.f) * k_multiply_factor;
+        // InfinityWard Engine (inherited from Quake) stores FOV as horizontal FOV at a 4:3
+        // reference aspect. Convert to true vertical FOV, then delegate to the
+        // standard vertical-FOV left-handed builder with the caller's actual
+        // aspect ratio.
+        //   vfov = 2 · atan( tan(hfov_4:3 / 2) / (4/3) )
+        constexpr float k_source_reference_aspect = 4.f / 3.f;
+        const float half_hfov_4_3 = angles::degrees_to_radians(field_of_view) / 2.f;
+        const float vfov_deg = angles::radians_to_degrees(
+                2.f * std::atan(std::tan(half_hfov_4_3) / k_source_reference_aspect));
 
         if (ndc_depth_range == NDCDepthRange::ZERO_TO_ONE)
-            return {
-                    {1.f / (aspect_ratio * fov_half_tan), 0, 0, 0},
-                    {0, 1.f / (fov_half_tan), 0, 0},
-                    {0, 0, far / (far - near), -(near * far) / (far - near)},
-                    {0, 0, 1, 0},
-            };
+            return mat_perspective_left_handed<
+                    float, MatStoreType::ROW_MAJOR, NDCDepthRange::ZERO_TO_ONE>(
+                    vfov_deg, aspect_ratio, near, far);
         if (ndc_depth_range == NDCDepthRange::NEGATIVE_ONE_TO_ONE)
-            return {
-                    {1.f / (aspect_ratio * fov_half_tan), 0, 0, 0},
-                    {0, 1.f / (fov_half_tan), 0, 0},
-                    {0, 0, (far + near) / (far - near), -(2.f * far * near) / (far - near)},
-                    {0, 0, 1, 0},
-            };
+            return mat_perspective_left_handed<
+                    float, MatStoreType::ROW_MAJOR, NDCDepthRange::NEGATIVE_ONE_TO_ONE>(
+                    vfov_deg, aspect_ratio, near, far);
         std::unreachable();
     };
 } // namespace omath::iw_engine