I doubt that square or round will make much difference. Here's the latest basket I made:
Not everyone has access to a roll that can roll 3/4-9 expando, though. Mine can just barely do it.
In my drum smoker this basket works just great. I dump in maybe 10 pounds of lump and start four or five fist-size chunks in a starter chimney over an outdoor propane burner and then dump the hot ones on top and put the drum all together. I can cook all day with that setup and only use maybe half the charcoal.
Thinking a little more, it might be that you're using Kingsford type fuel. When those bricquets get heavily ashed over they do cool down quite a bit. I tried cooking with those a couple times a few years ago on a different cooker. Back then I used to try to get them going again by blowing on them with pure oxygen from my cutting torch. Even doing that a surprising amount didn't work out well. I gave up on bricquets, especially when I saw the enormous volume of ash they leave behind.