Do you have airstones or pumps on the UGF? If you pumps you can stack the gravel a bit deeper than if your using air stones. Use a gravel that wont compact or get stuck in the plate slots..so not too small.
The whole idea is the pumps or airstones create current which brings the water through your gravel. So flow is the key. If you stack it too deep, then you will reduce flow through or make it too packed it wont filter properly.
As said, the dirt will get pulled and will collect under your UGF plate. The whole process worked for me many years ago with sucess. But eventually you need to get the gunk from under out. They also have reverse pumps which blow it through in reverse and the pumps have spnges so they filter dirt out before it goes down under your plate. This makes the current come up through the gravel.
I think it is a mess and not worth it. My opinion is use your 10 gallon filter on the 30g until you can get a HOB