Direct Fire with range exceeding 12

[triangular_cube]

Could I get some clarification on how this is actually played? It finally came up for the first time in a game last week and now I'm confusing myself.

Direct fire has to be self spotted, correct? So that a unit with a Direct Fire range (Heer 150mm IG for example) must be on a hill or otherwise increase its natural spotting range above 12 to fire at a target at ranges 13-15?

Or do they have implied optics that let them should out to 15 hexes regardless (sans SSR limiting spotting range)?

Like I said, I have now confused myself...