I wish I could help you, but my attempts at sourdough have all failed.
I think one of the reasons people use a tall container as opposed to a shorter one is that the sourdough starter rises. I've heard people talk about knowing when their starter's risen by looking at the side of the jar, even when it's risen and fallen again. I think maybe if you use a container with lower sides, if your starter rises, it might go over the top.
If no one here can help you, I suggest you go to this bread forum:
Forums | The Fresh Loaf