Well tac ops has an Extreme range rule. Which is not just for mortars but for all weapons. Is that what you are thinking about?
No, I found the thread after a few tries and I absolutely misread it. I still can't find anything about mortars on the noted pages, but it doesn't matter.
The handling of infantry mortars in the game infuriates me; I thought I saw a official-rules option to fix it and I went straight to my books and PDFs to try and find it and then here to ask why I couldn't find it. The rule never existed to begin with; that part of the thread was about mortars being *optionally* (!) indirect-fire weapons.
I was hoping for something else entirely, because mortars are practically worthless in game as they are now.