I've never understood why people put magnets at the back on their belt. If you're going to run magnets to hold mags, put them at the front where it's easy to throw mags on during table starts etc. Putting them at the back just makes it slow and awkward to do so. Or, use regular pouches and put magnets on the outside of them, at the front, for table starts.
I run 5 pouches and magnets on 3 of them, well now, two of them, one on the front of the first pouch, one on the side and then one on the side of the of the second pouch as well. I carry 61 rounds with me on a COF simply because of often needing to dump a mag after 2 or 3 shots in various parts of stages. I seldom need the last couple mags, but if sh!t goes sideways then they come in handy. When I am shooting overseas I run 4 pouches with the same magnet setup, and still carry 61 rounds total.