What your missing is the physical thickness of the overload.Overloads don't determine ride height. They don't even get used until there's enough weight on the rear end to introduce them to the perches.
But they're on TOP of the spring pack.
You are correct that sometimes their are overloads on the top that go against perches when enough weight is added on mostly 3500s and above but 2500s have them just on the bottom of the leaf pack and can be removed for more drop if wanted.
A lot of 2500's have them too. Most 2wds do not have the top over loads.
Never seen them myself on 2500s so I do stand corrected. Thanks!