I found the announcement post for the feature and it does state the nature of it’s exactness.
New Studio Feature - CollisionFidelity.PreciseConvexDecomposition (Enabled Globally):
I suggest that you break the floor into multiple chunked tiles because it will likely improve the quality of the approximations quicker than increasing the hole size. Splitting the floor into 4 unions will likely double the collision fidelity. And you could repeat this process if you need more. Also, increasing the hole sizes sounds like it would be a compromise to the artistic integrity, but chunking the floor is just a technical detail.