For a 10 round division, the worst case scenario is a stage that breaks down into 6 round positions. If the positions only had 5 rounds, you could just shoot 2 positions with the same mag. For a 32 round stage with 6 round positions, you'll need 5 mags. If it's an empty start, you'll need those 5 mags on your belt. I generally like an extra mag left on my belt for emergencies, so I bring a Barney mag to the line as well.
With magnets, I've moved my Barney mag out of my pocket and onto the magnet. I don't generally reload off the magnet on the clock during a stage that doesn't require it. So for me it's still 5 pouches and a magnet.
For single stack major, this logic works out to 6 pouches plus a magnet.
Number of pouches = 32 / ((capacity / 2)+1)