Unkown Units and Fortifications

[HMCS Rosthern]

I've noticed that if a unit becomes spotted, but not fully identified, i.e., is unknown and the unit is identified by a question mark, its current hot spot hex will show a fortification if one is present. Is there a rationale for this? For example, if artilllery is spotted from a distance (e.g. rocket artillery at night) how would the spotter be able to determine if there is a fortification?