How to insulate rim joist with radiator pipes?

Radiator lines sit about 1/2” off the rim joist. I was going to do 2" XPS with spray foam elsewhere.

Do I just do a small piece of 1/2” behind it? Not sure if I'm going to cause issues here by insulating

Radiator lines sit about 1/2” off the rim joist. I was going to do 2" XPS with spray foam elsewhere.

Do I just do a small piece of 1/2” behind it? Not sure if I'm going to cause issues here by insulating