I think what you have is exactly what I was thinking the screen would have been a layer between the rocks and the aquabloxs so the rocks didn't fall in to the water chamber but I suppose a better less clogging solution is larger rocks and then a layer of gravel.
Oh! Gotcha! We were concerned about the gravel falling through the Aquablox, so we added a layer (well, several layers!) of underlayment - one directly over the Aquablox and then several more layers as we added different sized gravel. Big mistake. We had to remove all of it - which involved shoveling and sorting many pounds of gravel - when we realized the underlayment clogs almost immediately. A power washer may have helped to clear the clogging, but we didn't have one at the time. It was really fine debris that was building up so it wasn't hard to clear, just annoying and constant.
We pulled the whole mess out and added a layer of softball sized boulders directly over the Aquablox, then we topped it with river stone - eliminated the pea gravel completely. I liked the look of the pea gravel - when it was clean - but it, too, clogged too easily. Plus the repeated raking meant we ended up with the larger gravel mixed with the pea gravel. We asked on one pond tour how the homeowner kept the pea gravel so clean and free of debris - they had someone come out and replace it every few weeks. Mmmmmm... no.
Now we rake it out every few weeks - easy to do and really more of an esthetic thing than a necessity.