Space diapers aren't known for clumping, and even diapers that are somewhat known for clumping usually do OK overnight. Clumping usually happens when you're walking or running, the movement in the diaper breaks up the padding and gravity pulls it down. (more quickly if your diaper is wet, but will happen eventually if dry) ALL diapers are going to do this, it's just a matter of how long it takes to happen.
That's weird you had this problem overnight. Do you squirm a LOT while you sleep? ("restless sleeper") Or maybe it got clumped a bit before bed - did you change into a fresh diaper right before bed, or did you go to bed in a worn, possibly wet diaper? There are some here that like going to bed in a wet diaper, but I personally always change before bed so I get max capacity and least wet time on my skin overnight.'
(and no, wearing adult underwear over a diaper doesn't do a lot to prevent clumping)
