Stencil portal partially showing to coincident meshes

I would like to have two meshes occupying the same position with a portal stencil intersecting them.

Only part of each mesh is visible through the portal. See images below.

I’ve tried using various playground examples, but I got nothing.

My feeble attempt is at https://playground.babylonjs.com/#R6IWZU#1

something like this?

Outstanding!

Thanks!