The indsutry standards for determining lift truck capacity in North America is based on a homogenous cube that is 48' x 48" x 48" where the HCG is at 24" and VCG is at 24" (in 41 year in this business I have foundthere are very few loads that have these characteristics). Any load size that has the CG greater than these will affect the rated lift capacity of the the unit. While the affects of an extended HCG can be "guesstimated" mathematically, an extended VCG can have a significant effect on the lateral (or side) stability of the unit, this is not so easily calculated.
So it is always best to veryify compliance to OSHA, ASME/ANSI with the OEM if you encounter a load that exceeds the nominal industry standards (either HCG or VCG).