Yeah well, I was responding to the context of your original post and questioning whether you really need to know the gameplay functions of the units to write your fanfiction. The short answer is no.
Eh, the point of most fanfiction is to allow the writer of such to focus on the aspects (and to embellish/exaggerate them usually) they find interesting about a particular IP - ie: fanwank.
No-one's going to be "distracted" by reading in your fanfiction that a unit hitting something it wouldn't normally hit because the gameplay isn't consistent with it. A reader of fanfiction knows there's going to be liberties being taken (or they should, rather...). If they do get annoyed about it, they're not the intended audience for your fanfic (ie: a person into "shipping" fanfic ain't gonna care). I don't really care how you treat the SC canon (I barely care for Sc canon and how Blizz treats it now generally - all the hate I've held for it has dissolved into apathy long ago) since I know it's fanfic at the end of the day.