What I was getting at was my solution opens up the sides to get better air flow. I don't think the room on the top will matter that much. With the shorter filters, the sides of the water shield is blocking the air flow.
Are you talking about the height of the trumpets inside the filter area being to close to the top? Maybe I mis-understood what your problem was? Would not be the first time.
Do you have room to run the ITG foam filters? They let air in from the top, which might help your situation.