diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index e115181..25ada38 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -1679,3 +1679,42 @@ alignment preference but a weak one.
 can be read as they are, and that they are sparse and variable-length rather than
 fixed-stride -- so the next attempt should look for a terminator-delimited walk
 through the sparse region, not for a record size.
+
+## Collision: the segmentation is not recoverable from zero structure
+
+Continuing on the verbatim payload, with the grid known.
+
+**Cells are not zero-separated.** Counting maximal runs of non-zero `u16` across
+the whole payload:
+
+    level 0   363 cells     15,115 runs     mean run 25.3 u16
+    level 1   384 cells     24,647 runs     mean run 51.5 u16
+    level 2    53 cells     31,512 runs     mean run 30.3 u16
+
+Two to three orders of magnitude apart, so a zero run is not a cell boundary.
+Cells are not uniform blocks either: level 0 averages 2,488 bytes per cell and
+level 2 averages 43,684, which cannot both be one fixed-size record.
+
+**The run lengths are not records.** Their histogram has a long tail of
+near-power-of-two values -- 2,140, 1,184, 840, 816, 628, 604, 562 -- which is
+what you get when a run is bounded by a single zero *byte* inside otherwise dense
+data, not by a delimiter. Combined with the 18%-zeros finding, the payload reads
+as dense data with sparse holes rather than as a delimited sequence.
+
+**So: not ascending `u32` tables, not zero-run delimiters, not fixed stride.**
+All three segmentation theories are now excluded on the full population rather
+than on a sample.
+
+### What would actually unblock this
+
+`overlay.bin` **is the game's own code**, and the collision parser is in it --
+`Camera_CollPrimTest WARNING! - grid out of bounds! (RAR)` was located in the
+debug string pool earlier, and that string is inside the collision routine. The
+format is therefore recoverable, but not by measuring bytes: it needs either
+disassembly of that routine or a reference for R&C2's collision cell record.
+
+Stating this plainly is worth more than another scan. The disc-side measurement
+space for collision is now genuinely exhausted -- the bytes are available, they
+are verbatim, the grid is known, and three independent segmentation theories have
+failed on the whole population. Further probing without the loader's own logic is
+not going to converge.