How to unite objects with assembly mode?

Hi everyone,

I'm modelling coils using the Multi-Turn Coil Domain, and I'm having trouble getting the magnetic fields to work when I finalize the geometry with an assembly (I need to use assembly mode because I need to import some CAD files with very complex geometry). I'm doing a frequency domain study.

I've got a cylindrical coil surrounded by a spherical domain of air (see attached file). The problem seems to be that the Magnetic Insulation boundary condition is automatically applied to the boundaries of the coil, so the magnetic fields are trapped inside. But I can't figure out how to get rid of it. When I do a Form Union instead, the Magnetic Insulation is only applied to the boundaries of the sphere, which is what I want.

I think the reason it's not working in assembly mode is because the coil and the air sphere need to be linked/continuous, but how do I do this? Does it involve pairs somehow? I've tried applying an Identity pair between the boundaries of the coil and sphere, but that didn't work. Then I applied continuity to the pair, but it still didn't work. I've also tried adding a Boolean Operations > Union to the geometry, but that didn't work either.

Can anyone please help me?

Thanks in advance,

Neil