I'm using the updated map.
A brown position group runs through hexes 1213(D13),1114(D8),1115(D7),1116(D6).
There's a Japanese unit in D8, and US units in D6 and hex 1215, which contains an intense fire brown dot at the point where it and hexes 1115(D7) and 1116(D6)meet.
In the Japanese fire phase, the card has a brown square. Does the US unit in hex 1215 take a step loss?
Yes, it does. As long as one of the position group hexes is occupied by an undisrupted Japanese unit, all brown fire dots are "active".
Another question - hexes 1815 and 1816 form a green position group, but neither hex contains a green fire dot. Does this mean that if the hex position group contained both US and Japanese units (not Close Combat) they have no FoF on each other?
It's one of those wonderful hexes where you can fire but the Japanese can't fire back. Enjoy! (At least until that A, P or M action shows up...)