As far as I know, that's not a mechanic currently in the game. Targeting non-marker terrain would include targeting aura terrain, which is somewhat under defined. (Being in an aura is easy to determine. Trying to determine where the aura's base is, if you have nearby terrain, isn't...)
Personally, I don't think "When drawing LoS to a Marker, the Marker is treated as a model with Size 0, unless the Marker has the Height Terrain Trait, in which case its Size is equal to its Height." is supposed to mean, essentially "Draw line of sight to the marker as if it had Sz equal to its Ht (0, default)" without triggering side effects. (We managed to beat almost all of the unnecessary uses of "model" out of the line of sight system during the beta, but it looks like this one was missed.)
Because leads to claiming that Take the Hit ("After an enemy model targets a friendly model within 2 ..." and someone targeted a friendly terrain marker) or having Challenge being used to prevent targeting a marker.