I would really not rely on many of those results. Mag at 1400 in IO, I don't think so, 1100 to 1200 from what I remember is more realistic, unless they got a bad batch of salt or mixed it at very high concentrations.
To be honest, your initial question has to many variables, because of the batch of IO salt you have, your salinity levels, the type of water you are using to mix the salt with, etc. You need to get a Mag test kit and test you levels from your batch of salt water you are making. That is the only reliable way to know how to adjust your levels. Anything else would be guessing and cause you more problems. There is a chem forum on RC with a person that has done many excellent articles. Do a search there if you are just looking for a baseline, but again if you don't test it don't add things to adjust it. You also need to test your tanks water levels, because if you start making major adjustments you need to do it slowly or you could kill your current inhabitants.