The burn pot stacks inside the kettle for storage and transport so it has to be an inverse conical shape so it fits in, if that's what you mean?Not having seen one in action, but why in both makes is the burn chamber smaller than the diameter of the kettle? I see the Petromax has stabilising legs, but having a smaller chamber at the bottom on both seems to make everything unnecessarily unstable?
I have the stabilising legs for my smaller ghillie kettle and find they work quite well. Once the kettle is off the burn pot it's very stable as the base is the widest point, but tbh I've never had a problem with stability. It's no different to making sure you have a small gas stove level and stable before you put a pot on top. The main benefit of the legs on the stand IMHO is that it raises the burn pot off the ground.