These are very good questions if you are depending on a stacker to handle the stated capacity at its very max raised height.  For instance, if you are looking to purchase a stacker with a maximum fork height of 65” and a 2,200 lb maximum capacity then make sure that it will be able to handle 2,200 lbs at 65”.  At www.material-handling.com we have made it clear that if there are any changes in the capacity it will be stated in the Tech Spec section under the subcategory titled “Capacity Range”.  If a stacker has a capacity range then it is wise to disclose it.  For example, the PPS2200-150AS is a powered stacker that is rated at 2,200 lbs.  The maximum raised fork height is 150”.  That is 12.5 feet high.  If you go to the Tech Specs tab and look at the Capacity Range you will notice the following:  (1) 0" - 84": 2,200 lbs; (2) 85" - 96": 1,800 lbs; (3) 97" - 120": 1,500 lbs; (4) 121" - 144": 1,200 lbs

Here is what this means: From 0 – 84 inches the capacity that PPS2200-150AS can handle is 2,200 lbs.  From 85 inches to 96 inches the capacity of the Power Stacker de-rates to 1,800 lbs.  From 97 inches to 120 inches the capacity de-rates to 1,500 lbs and from 121 inches to 144 inches the capacity is 1,200 lbs.  At the maximum fork height the capacity of the PPS2200-150AS is 1,200 lbs.  With this information you can determine if this stacker is suitable for your application.