No, sorry, but you're wrong. You can also take damage while on the wall side of a rune. Gotta be fast to be safe. Several times I've taken big electric damage while I felt I should have been "safe", and either got interrupted or even killed (not (yet) on HCL) while deactivating a run on the side of the run away from the center.
As an fyi, you can also take damage while in one of the "in-between" stretches, after deactivating the last rune and waiting to time the next (gotta be further back than half-way in one of those stretches).