So I am not sure if I am doing something wrong,
but if I pipe a terrain into a simple OBJ HDA with a Geo node that just does a Heightfield Convert, I get the result at 0,0,0 instead of with the correct offset.

Now if I do it with a SOP subnet turned into HDA it works perfectly fine, unfortunately I need to use the unity_instance method so gotta keep my HDA as OBJ.

Hmm, are you able to post your HDA or show your network? Usually the object merge handles how the transform is applied, using the Keep World Transform setting from the input field UI.

Yes should have posted that!
Here you go.

I am on Unity 2018.3.0b2
Houdini 16.5.668

I just added a mesh object too to make sure that behaved as expected

In your HDA, change the terrain OBJ's object merge's Transform type to “Into this Object”.

That did it! Thanks!