We've added frame extensions to the Evolution. In my opinion this makes the Evo the best backpack made - PERIOD.
The extensions allow you to use the pack in a 24" height or a 28" height. 24" is great for going through brush and under limbs, or for lightweight backpacking. The extensions are better for hauling heavy loads because you can get a steeper load lifter angle plus the higher frame allows you to load the pack a bit higher and get the center of gravity up behind your shoulder blades where it belongs.
This will be a standard upgrade option. We will offer the 28" solid frame plus the 24" with extensions. The solid frame can be retrofitted later to work with the extensions.