On -X, it is not a perfect mirror. Here is a view you guys are familiar with, the end in 3d plotted by E, X, and N.
-X is much smaller and compact. A different pattern.
Here they are together.
The line across E0, X0 is a bug, but can anyone else confirm that no cells exist with N= -1 for +E?
Sorry, can anyone else confirm that cells don't exist where X = -1?
Checked again. Yes, this is all combinations of E, X, and N using my bruteforce cell creation method.
And correct again, I'm saying formula applies in cells that aren't valid but I can also say the formula always applies in cells that are valid. At least where E>=0, but for any X (positive or negative) and any N < 0.