diff --git a/src/libslic3r/Geometry.hpp b/src/libslic3r/Geometry.hpp
index 11d405e4c2..7c670bb7c6 100644
--- a/src/libslic3r/Geometry.hpp
+++ b/src/libslic3r/Geometry.hpp
@@ -86,7 +86,7 @@ static inline bool is_ccw(const Polygon &poly)
 
 #if ENABLE_OUT_OF_BED_DETECTION_IMPROVEMENTS
 // returns true if the given polygons are identical
-static bool are_approx(const Polygon& lhs, const Polygon& rhs)
+static inline bool are_approx(const Polygon& lhs, const Polygon& rhs)
 {
     if (lhs.points.size() != rhs.points.size())
         return false;
diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 4546444eed..73661723a0 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -1566,12 +1566,14 @@ unsigned int ModelObject::check_instances_print_volume_state(const Polygon& prin
         unsigned int inside_outside = 0;
         for (const ModelVolume* vol : this->volumes)
             if (vol->is_model_part()) {
+                const Transform3d matrix = model_instance->get_matrix() * vol->get_matrix();
 #if ENABLE_FIX_SINKING_OBJECT_OUT_OF_BED_DETECTION
-                const BoundingBoxf3 bb = vol->mesh().transformed_bounding_box(model_instance->get_matrix() * vol->get_matrix(), 0.0);
+                const BoundingBoxf3 bb = vol->mesh().transformed_bounding_box(matrix, 0.0);
 #else
-                const BoundingBoxf3 bb = vol->get_convex_hull().transformed_bounding_box(model_instance->get_matrix() * vol->get_matrix());
+                const BoundingBoxf3 bb = vol->get_convex_hull().transformed_bounding_box(matrix);
 #endif // ENABLE_FIX_SINKING_OBJECT_OUT_OF_BED_DETECTION
-                ModelInstanceEPrintVolumeState state = printbed_collision_state(printbed_shape, print_volume_height, bb);
+                const Polygon volume_hull_2d = its_convex_hull_2d_above(vol->mesh().its, matrix.cast<float>(), 0.0f);
+                ModelInstanceEPrintVolumeState state = printbed_collision_state(printbed_shape, print_volume_height, volume_hull_2d, bb.min.z(), bb.max.z());
                 if (state == ModelInstancePVS_Inside)
                     inside_outside |= INSIDE;
                 else if (state == ModelInstancePVS_Fully_Outside)
diff --git a/src/libslic3r/Technologies.hpp b/src/libslic3r/Technologies.hpp
index c096dfcf6d..365493a66b 100644
--- a/src/libslic3r/Technologies.hpp
+++ b/src/libslic3r/Technologies.hpp
@@ -71,8 +71,15 @@
 
 // Enable fixing loading of gcode files generated with SuperSlicer in GCodeViewer
 #define ENABLE_FIX_SUPERSLICER_GCODE_IMPORT (1 && ENABLE_2_4_0_ALPHA3)
+
+
+//====================
+// 2.4.0.alpha4 techs
+//====================
+#define ENABLE_2_4_0_ALPHA4 1
+
 // Enable the fix for the detection of the out of bed state for sinking objects
-#define ENABLE_FIX_SINKING_OBJECT_OUT_OF_BED_DETECTION (1 && ENABLE_2_4_0_ALPHA3)
+#define ENABLE_FIX_SINKING_OBJECT_OUT_OF_BED_DETECTION (1 && ENABLE_2_4_0_ALPHA4)
 // Enable detection of out of bed using the bed perimeter and other improvements
 #define ENABLE_OUT_OF_BED_DETECTION_IMPROVEMENTS (1 && ENABLE_FIX_SINKING_OBJECT_OUT_OF_BED_DETECTION)