The plate doesn't have to cover the whole base of the tank Aqua, very few will. As long as most of it is covered, as yours is, things will be fine.
It is so long since I bought filters and stuff I originally forgot the UGF these days have a cartridge on top of the uplift. Never saw the point in them myself. As I think John said, someone added them as a sales gimmick I guess.
The older UGFs with the thin uplifts didn't have an airstone in them either. It wasn't until they started making them with the fatter uplifts that they added the airstone.