3D carving foam vs foamcore

Hello all, I finished carving my first project back in May at the local maker space, a terrain model. Based on information I gleaned from here (thank you all!) and other places (including the advice of the main helper at the maker space), I chose to purchase HDU duna corafoam 15#.

While corafoam is amazing at taking intricate detail, in retrospect I think it was overkill, as I covered most of the surface with railroad model grass and gravel. So for my next project I'm looking at alternatives.

Have any of you 3D carved Ultraboard? I received a sample today and I'm going to test it. The technical spec sheet states it is millable but I'm thinking the intention is 2D cuts for letters, not really for 3D carving.

I don't want to use EPS - the giant beads of foam would be rougher than I want. XPS seems to be not available locally at the small quantities I need (crate + shipping fees makes it more expensive than the corafoam my local supplier carries in-stock). I'm not sure what the filler is in the middle of the Ultraboard - honestly it looks like EPS when I poke it with my fingernail, but it does have a finer grain. It's almost... crispy? (I got a 2" thick sample)

The milled corafoam, bare: https://goo.gl/photos/j7bHgLyBaV38uZhY8
With paint & surface application: https://goo.gl/photos/SGaC3kS75RHkWXyT6

No experience in what you are doing but you might try the blue or pink insulation foam from the big lumber yard. When covered the softness may not matter. Just a thought.