diff --git a/docs/report/013.ipynb b/docs/report/013.ipynb
index 87a8e204..7f948a51 100644
--- a/docs/report/013.ipynb
+++ b/docs/report/013.ipynb
@@ -10000,7 +10000,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Compare with [Figure 2](https://downloads.hindawi.com/journals/ahep/2020/6674595.pdf#page=9)."
+    "Compare with [Figure 2](https://downloads.hindawi.com/journals/ahep/2020/6674595.pdf#page=9). Note that the distributions differ close to threshold, because the distributions in the paper are produced [with form factors](https://ampform.readthedocs.io/en/0.12.x/api/ampform.dynamics.html#ampform.dynamics.relativistic_breit_wigner_with_ff) and an [energy-dependent width](https://ampform.readthedocs.io/en/0.12.x/api/ampform.dynamics.html#ampform.dynamics.EnergyDependentWidth)."
    ]
   }
  ],