For one thing, you will never reach the claimed absorbency of a diaper when you wear and use it. Those tests represent an absolute best case scenario, with virtually every variable removed.
When you’re wearing a diaper and using it, physics kicks in. When you go, you’re not distributing evenly around the diaper, you’re confined to a much smaller are that from there the liquid will wick and spread outward. Then you have gravity playing against you, to where it will only wick so far depending on how your body is positioned. On top of that, the longer you have a diaper on, the more the material inside breaks down or absorbs sweat, oil, and other body secretions, biting into the absorbency. There are other factors that contribute, but for the most part, these are the big ones.
Now, if you play your cards right, you could squeeze a little more life out of a diaper once it gets close to full or leaking, but it’s hit or miss. Regardless, you won’t ever hit the claimed absorbency rating.
I would however suggest that there are better diapers to use for what you’re trying to achieve. Northshore MegaMax and ABU PeekABU/Simple Ultra hold more and swell more. They would get you closer to your goal.