I actually like the fact that the plate fits into the table slightly. I have had the oak park table for about four years now, and it has loosened up some, but is still nice and snug. I think this gives more accuracy. My previous table with an insert was one I had made, and I had oversized the cut just a tad too much and it was awful. I ended up using body filler to tighten the hole up some. When I had my router table in the extension wing of my table saw, it was bolted up tightly, but a pain to change bits. The tight insert in the oak park table is a happy medium in my humble opinion.
If you find you just have to loosen things up a bit, I would recommend lightly sanding one side of your insert plate and see what happens.