Collider seems bigger than it is

As you can see below I have 2 boxes with both of them colliders attached. I have also attached a rigidbody and a script that listens to OnCollisionEnter on the blue box. If the blue box collides with the red one it should move away. This does work but it triggers way to soon. What could be the cause of this

Many thanks in advance!

I was having the same issue and found that changing the offset fixed the issue in my case.

Go to

Edit > Project Settings > Physics > Default Contact Offset and make sure this value is set to 0.01.