Help: Large objects falling through landscape

I’m working on a first person game that uses very large simulated cubes that are attracted to the player as enemies. If they are large enough they tend to fall through the landscape. It seems like anything over 20m in size tends to have issues. Particularly if there is any extra downward velocity on the cubes (like explosive force).

Are there any parameters I could tweak to get better simulations? Would scaling my world down help solve the issue?

Here are my physics settings: