diff --git a/src/libslic3r/Fill/FillRectilinear2.cpp b/src/libslic3r/Fill/FillRectilinear2.cpp
index 242923589..8beff03be 100644
--- a/src/libslic3r/Fill/FillRectilinear2.cpp
+++ b/src/libslic3r/Fill/FillRectilinear2.cpp
@@ -1853,7 +1853,7 @@ FillRectilinear2WGapFill::fill_surface_extrusion(const Surface *surface, const F
         double min = 0.2 * params.flow->scaled_width() * (1 - INSET_OVERLAP_TOLERANCE);
         double max = 2. * params.flow->scaled_width();
         // collapse 
-        double min_offset = 0.2 * params.flow->scaled_width() * (1 - INSET_OVERLAP_TOLERANCE);
+        double min_offset = 0.1 * params.flow->scaled_width() * (1 - INSET_OVERLAP_TOLERANCE);
         //be sure we don't gapfill where the perimeters are already touching each other (negative spacing).
         min = std::max(min, double(Flow::new_from_spacing(EPSILON, params.flow->nozzle_diameter , params.flow->height, false).scaled_width()));
         double max_offset = 2. * params.flow->scaled_spacing();
diff --git a/src/test/libslic3r/test_extrusion_entity.cpp b/src/test/libslic3r/test_extrusion_entity.cpp
new file mode 100644
index 000000000..0550d1c23
--- /dev/null
+++ b/src/test/libslic3r/test_extrusion_entity.cpp
@@ -0,0 +1,84 @@
+
+//#define CATCH_CONFIG_DISABLE
+
+#include <catch.hpp>
+#include <string>
+#include "../test_data.hpp"
+#include "../../libslic3r/libslic3r.h"
+#include "../../libslic3r/ExtrusionEntityCollection.hpp"
+#include "../../libslic3r/ExtrusionEntity.hpp"
+#include "../../libslic3r/Point.hpp"
+#include <cstdlib>
+
+Slic3r::Point random_point(float LO=-50, float HI=50) {
+    float x = LO + static_cast <float> (rand()) /( static_cast <float> (RAND_MAX/(HI-LO)));
+    float y = LO + static_cast <float> (rand()) /( static_cast <float> (RAND_MAX/(HI-LO)));
+    return Slic3r::Point(x, y);
+}
+
+// build a sample extrusion entity collection with random start and end points.
+Slic3r::ExtrusionPath random_path(size_t length = 20, float LO=-50, float HI=50) {
+    Slic3r::ExtrusionPath t { Slic3r::ExtrusionRole::erPerimeter, 1.0, 1.0, 1.0};
+    for (size_t j = 0; j < length; j++) {
+        t.polyline.append(random_point(LO, HI));
+    }
+    return t;
+}
+
+Slic3r::ExtrusionPaths random_paths(size_t count=10, size_t length=20, float LO=-50, float HI=50) {
+    Slic3r::ExtrusionPaths p;
+    for (size_t i = 0; i < count; i++)
+        p.push_back(random_path(length, LO, HI));
+    return p;
+}
+
+using namespace Slic3r;
+
+SCENARIO("ExtrusionEntityCollection: Polygon flattening") {
+    srand(0xDEADBEEF); // consistent seed for test reproducibility.
+
+    // Generate one specific random path set and save it for later comparison
+    Slic3r::ExtrusionPaths nosort_path_set {random_paths()};
+
+    Slic3r::ExtrusionEntityCollection sub_nosort;
+    sub_nosort.append(nosort_path_set);
+    sub_nosort.no_sort = true;
+
+    Slic3r::ExtrusionEntityCollection sub_sort;
+    sub_sort.no_sort = false;
+    sub_sort.append(random_paths());
+
+
+    GIVEN("A Extrusion Entity Collection with a child that has one child that is marked as no-sort") {
+        Slic3r::ExtrusionEntityCollection sample;
+
+        sample.append(sub_sort);
+        sample.append(sub_nosort);
+        sample.append(sub_sort);
+        WHEN("The EEC is flattened with default options (preserve_order=false)") {
+            Slic3r::ExtrusionEntityCollection output = Slic3r::FlatenEntities(false).flatten(sample);
+            THEN("The output EEC contains no Extrusion Entity Collections") {
+                CHECK(std::count_if(output.entities.cbegin(), output.entities.cend(), [=](const ExtrusionEntity* e) {return e->is_collection();}) == 0);
+            }
+        }
+        WHEN("The EEC is flattened with preservation (preserve_order=true)") {
+            Slic3r::ExtrusionEntityCollection output = Slic3r::FlatenEntities(true).flatten(sample);
+            THEN("The output EECs contains one EEC.") {
+                CHECK(std::count_if(output.entities.cbegin(), output.entities.cend(), [=](const ExtrusionEntity* e) {return e->is_collection();}) == 1);
+            }
+            AND_THEN("The ordered EEC contains the same order of elements than the original") {
+                // find the entity in the collection
+                for (auto e : output.entities) {
+                    if (!e->is_collection()) continue;
+                    Slic3r::ExtrusionEntityCollection* temp = dynamic_cast<ExtrusionEntityCollection*>(e);
+                    // check each Extrusion path against nosort_path_set to see if the first and last match the same
+                    CHECK(nosort_path_set.size() == temp->entities.size());
+                    for (size_t i = 0; i < nosort_path_set.size(); i++) {
+                        CHECK(temp->entities[i]->first_point() == nosort_path_set[i].first_point());
+                        CHECK(temp->entities[i]->last_point() == nosort_path_set[i].last_point());
+                    }
+                }
+            }
+        }
+    }
+}