Hi Paul - I admire your optimism and hope. But the meniscus is always there no matter how you look at it and fill it. Its a physical fact of surface tension, surface wetting and surface/air interaction etc. All threads that are honest about the epoxy levelling experience have poor results.
Even if you cast the perfect surface you still have a soft foundation for your mill parts and that's the major concern. Model a 6mm steel plate, 6mm epoxy and the rail with a counterbore hole. Push down on that hole with the required bolt preload and see how far the epoxy compresses.... Not pretty... Peter