...
51 were CAL events that had backsplash which triggered the TKR and just didn't happen to hit a tile
2 hit the space-craft and interacted causing backsplash.
So that leaves us with 216 to consider.
...
64 of the remaining events did have at least one MC "hit" within a tile.., but the tile was determined to be below threshold by the digitization algorithm.
18 had MC "hits" in ribbons that were determined to be below threshold in the digitization algorithm (though we should note that the algorithm for the ribbons needs adjustment - namely in terms of the mean number of PEs by position along the ribbon)
Of the 134 that failed to go through any active material in the ACD:
115 slipped through the gaps along the corners where the side tiles meet.
16 went through between two columns of side tiles on the same face...but didn't' seem to go through a ribbon.. need to look at those a bit more closely I suspect.
3 seemingly fell through some gap in top