Pretty sure the lip is not the cause. At the sunbeam course the machines they used had the smooth lip and they leaked A LOT.
First thing Id do is make sure you are locking your group handle in firm enough and failing that Id check your group head seal (blue seal) for wear. If that is fine check the locking collar itself for signs of wear (plenty of threads explaining this in detail). Remember the smallest amount of wear and/or coffee build up around the seals and collar can be enough to cause leaks.
In my experience the blue group head seals last about 9 months before they start to wear enough to leak small amounts of water.