Hopefully someone who has more experience with your diet and the forms/amounts of your medicines will reply, BUT...

Bowel tolerance of magnesium compounds can be affected by a wide list things. Taking calcium at the same time (or in the same time period) as magnesium helps to reduce the bowel flushing effect. Whether or not that means you need more magnesium is a good question - though it doesn't necessarily mean you're absorbing all of the magnesium.

High-macro diets (high protein, carbohydrate, fat) can also make more use of magnesium, especially when the ratios are radically different. (ex: 1:2:12 protein carb fat)

If I were you, I'd keep going with your current amounts and be patient with the results. Unless you're trying to flush your bowels, not having that effect is in my opinion a good thing. It all really depends on your personal state of being. Having said that, don't be afraid to experiment a little bit - but if you do experiment, as always, alter the amounts gradually. Last thing: the idea with supplementation is to get to a point where you don't need the supplement anymore, so taking occasional 1-2 day breaks to assess your health progress can really help to determine dosage.