Hi,
Stock Cherokee tank, and most other 4wd too, has considerable expansion, maybe I think 20%, capacity to be sure the charcoal can doesn't flood. This has been the case since sealed vapour tanks became law in the 1970s.
If you park at the right angle, shake the car etc etc, you can often get a bit more fuel into this air pocket.
Marcus ohms (
www.gojeep.rockcrawler.com) has modified the breather in his tank to take advantage of the air space. See his website for details of how to get the extra capacity. If you really want capacity try the 120L Long ranger tank, although is does hang low, best to only fit if you have some lift.