Missanna, a useful way to look at plant nutrients is in terms of plant response to different levels of supplied nutrients. A useful paper in this regard is by Rebecca Bichsel et al., 2008, it can be downloaded for free at Nitrogen, Phosphorus, and Potassium Requirements for Optimizing Growth and Flowering of the Nobile Dendrobium as a Potted Orchid The take-away (at least for me) from this paper is that N and K are needed in greater supply than P. The paper focuses mainly on N, P and K, but where they do mention Ca, the researchers seem to be applying it at about the same rate as N in fertilizer solution, and Mg at half that strength.
If you have not seen them already, the St. Augustine Orchid Society St. Augustine Orchid Society - North Florida Orchid Growing makes available on its web page some good reading on orchid culture. Scroll to the bottom of their home page, There is a heading on "Orchid Culture", with topics in 5 sub-groups. In the first group, 5th star from the top, there is a section on water quality and fertilizers. Within that section you will see an article by Sue Bottom on Ca and Mg, also, a series of 5 articles by Bill Argo, the 3rd of which is on fertilizers and nutrients.