Just a bit of food for thought when considering applying (or not applying) the "rules of thumb" in quesstimating the capacity at an extended load centers, it seem every one starts with the base rated capacity of the machine (3000, 4000 (kg or lbs) etc.

In the US 3000 to 6500lb base capacity cushion, pneuamtic or electric forklifts are most commonly (80%+) equipped with a 4.8 meter (188") triple mast and side shifter and typically the net capacity of this machine is 400 - 600 lbs less than the base of the machine. This is the point from which any derating guesstimates needs to start.