Hexagons are hard to find, but the idea behind straight sides is more springs and more of the tension pushes down the seams to the sweet spot in the middle of the tarp(jumping surface). Whereas the circle spreads it evenly around the springs instea of the middle area. So basically stay away from round sides and you're set. Its like a sheet, of 2 people used both of their hands to hold up a circle cloth or blanket, it would sag evenly throughout the middle. But with a hexagon, if both people only held 4 corners, it allows a slightly more taut rectangle surface. It may be hard to imagine, but stay away from circle