I use
KRISPIN's Formula to Calculate Magnesium Daily Requirement-
only about 4% of magnesium oxide is absorbed that is why it's good as a laxative the magnesium oxide remains in the digestive tract, absorbs water and softens stools. You get a high absorption but still good laxative value from magnesium citrate so it can be used for both. But the best forms (albion patent mineral chelates) don't have a laxative effect because more of the magnesium is absorbed therefore there is less left to attract water and soften stools.

If dancinbr isn't having problems with runny stools then he's probably not taking too much though it's more than I take but I'm not a diagnosed diabetic and he is and that probably accounts for the extra magnesium requirement.

98% of your magnesium stores should be locked in your skeleton, when you are becoming diabetic your body will raid those stores for a long time so until you become diabetic you probably (because plasma magnesium tests only measure the 2% circulating not the 98% that should be stored in bones, ) manage, but once those stores are depleted it will take as long to replete them and you will need more magnesium daily than your typical daily needs.

If you're poor and have huge debts you need to earn MORE money daily than the bank charges and essentials shopping bills, to get rid of the debt and have spare money in bank requires considerably more income than a person with no debt.

Same with magnesium accounting.
The turnover in bone cells is probably over a 10yr time frame so to rebuild bones with the optimum amount of magnesium will require a diabetic to be in magnesium surplus (that means more magnesium daily than essential for daily needs but not too much to cause the runs) for at least 10yrs.